Cable Support Spacing: Clips, Conduit and Trunking

Ask how far apart cable clips go and someone will find you a table. It is a good table, it is in the On-Site Guide, and it has been in every edition for decades. What it will not tell you is that it only answers half the question.

BS 7671 asks two separate things of a support. Regulation 522.8.5 wants the wiring system held up so that it is not damaged by its own weight. Regulation 521.10.202 wants it held up so that it will not be liable to premature collapse in the event of fire. Those are different loads, different temperatures and different answers — and the IET is explicit that the tables address the first one only.

The short version: the On-Site Guide Appendix D spacing tables give examples that meet Chapter 52 and, in the IET's own words, not the specific requirements of Regulation 521.10.202. Read your spacing off the table for the weight duty. Then work the fire duty separately, because at two hours a support channel keeps about a fifth of its strength and a steel drop rod is allowed between 6 and 10 per cent of its ambient stress — and closing the brackets, which only reduces the load in proportion, cannot make that up.

Each section below ends with a tickable checklist of what to confirm at that stage, with the clause it comes from beside it — nine of them, covering the whole of Section 8 of the IET Guide to Cables and Cable Management: choosing the system, materials and corrosion, external influences, spacing, the load calculation, the forces beyond dead weight, the fire condition, IP and IK, and what ends up on the drawing. The page prints with the boxes empty if you want to carry it round a job.

Try it: the support spacing explorer

Pick what you are supporting and the explorer reads the Appendix D spacing, builds the load that spacing puts on one bracket, and then asks what carries it — at ambient and at each fire duration, on both of the published stress sets. Everything here runs on the same modules as the MEP bracket calculator and the containment fill calculator.

Two duties, two numbers

The tables are guidance against Chapter 52, and they say so. The wording in the IET's guidance is worth quoting because it is so easily skipped: the spacings contained in these tables “provide examples that will meet the requirements of Chapter 52 of BS 7671 and not the specific requirements of Regulation 521.10.202”. Chapter 52 is selection and erection — weight, mechanical stress, the ordinary service condition. That is a real duty and the table discharges it properly.

Regulation 521.10.202 is the other one, and it is broader than most people assume. It applies to all wiring systems without exception — including metallic telephony and small-core fibre, which the guidance calls out specifically because they may have a low melting point. The concern is not the cable. It is what a curtain of dropped cable does to people trying to leave a building and to firefighters trying to enter it. Cables installed in or on steel containment systems are deemed to meet the regulation, which is why the fire question so often becomes a containment question rather than a clipping one.

So on any job with fire-rated circuits you end up with two spacings. They are not alternatives and the shorter one is not automatically right either — they answer different questions, and the design has to satisfy both.

Checklist: which duty am I answering?

Confirmed the wiring system is supported against damage by its own weight.Reg 522.8.5
Confirmed supports will not be liable to premature collapse in fire — for every wiring system on the job, including metallic telephony and small-core fibre.Reg 521.10.202
Identified which runs are fire-rated, and for what duration.Section 8.4.2
Noted where cables are in or on steel containment, which is deemed to meet the fire support requirement.Reg 521.10.202 NOTE 2
Recorded that any spacing taken from the tables answers Chapter 52 and not Regulation 521.10.202.Section 8.5

What the tables actually say

Table D1 is a step function. Clip spacing is banded by the cable's overall diameter, and inside a band nothing changes. Cross a boundary by a tenth of a millimetre and the spacing moves. This is why substituting a cable late in a job is not always neutral: a slightly fatter equivalent can push a run into the next band.

A step chart of On-Site Guide Table D1 with cable overall diameter on the horizontal axis and maximum clip spacing in millimetres on the vertical, showing horizontal spacings stepping 250, 300, 350 and 400 and vertical spacings 400, 400, 450 and 550 across the four diameter bands, with a dashed marker where the table ends at 40 millimetres. — Table D1 is a step function, not a curve. A cable a tenth of a millimetre wider can cross a band boundary and change the spacing — and above 40 mm the table simply stops.

Maximum spacing of clips, millimetres — On-Site Guide Table D1
Cable	d ≤ 9 mm		9 < d ≤ 15 mm		15 < d ≤ 20 mm		20 < d ≤ 40 mm
Cable	Horiz.	Vert.	Horiz.	Vert.	Horiz.	Vert.	Horiz.	Vert.
Non-armoured thermosetting or PVC sheathed	250	400	300	400	350	450	400	550
Armoured	–	–	350	450	400	550	450	600
Mineral insulated or aluminium sheathed	600	800	900	1200	1500	2000	–	–

A dash is not “no limit”. It means the table does not cover that combination — armoured cable below 9 mm, mineral insulated above 20 mm — and you go to the manufacturer, not to the column next door.

Three notes under that table carry as much weight as the numbers. The first is the one most often read backwards: the horizontal spacings may be applied to runs at more than 30° from the vertical, and the vertical spacings apply only within 30° of vertical. A run at 45° is therefore a horizontal run for this purpose, and takes the tighter figure. The second: a flat cable is banded on its major axis, not on an equivalent round diameter. The third: above 40 mm overall diameter the table stops and the manufacturer's recommendation governs — it does not simply continue at 400 mm.

Conduit and trunking have their own tables, and both are in metres where Table D1 is in millimetres. That unit change is a genuine trap when the three tables are being read in the same sitting.

Two grouped bar charts in metres. On the left, conduit support spacing by nominal diameter band comparing rigid metal against pliable conduit, rigid metal reaching 2.25 metres where pliable reaches only 0.8. On the right, trunking support spacing by cross-sectional area band comparing metal against insulating trunking, metal reaching 3 metres and insulating 1.75. — Pliable conduit spans about a third of what rigid metal does, and insulating trunking little more than half of metal. The containment that carries none of its own load is the one that needs the supports.

Maximum distance between supports, metres — conduit (Table D3) by nominal diameter
Conduit	d ≤ 16 mm		16 < d ≤ 25 mm		25 < d ≤ 40 mm		d > 40 mm
Conduit	Horiz.	Vert.	Horiz.	Vert.	Horiz.	Vert.	Horiz.	Vert.
Rigid metal	0.75	1	1.75	2	2	2.25	2.25	2.5
Rigid insulating	0.75	1	1.5	1.75	1.75	2	2	2
Pliable	0.3	0.5	0.4	0.6	0.6	0.8	0.8	1

Maximum distance between supports, metres — cable trunking (Table D4) by cross-sectional area, mm²
Trunking	300 < A ≤ 700		700 < A ≤ 1500		1500 < A ≤ 2500		2500 < A ≤ 5000		A > 5000
Trunking	Horiz.	Vert.	Horiz.	Vert.	Horiz.	Vert.	Horiz.	Vert.	Horiz.	Vert.
Metal	0.75	1	1.25	1.5	1.75	2	3	3	3	3
Insulating	0.5	0.5	0.5	0.5	1.25	1.25	1.5	2	1.75	2

Pliable conduit spans about a third of what rigid metal does, in every band. It carries none of its own load, so the supports carry all of it.

Two more rules sit under those tables. Supports go within 300 mm of a bend or fitting — the tabulated span is for straight run, and a bend is where the pull is. And the inner radius of a conduit bend is not less than 2.5 times the outside diameter, which is a cable-protection rule that quietly constrains where the next support can physically go.

What Appendix D does not tabulate is worth listing, because the absence is often read as permission. There is nothing for cable tray, ladder or basket — those are sized on the manufacturer's load and deflection curves to BS EN 61537, and the end span of a run deflects more than the inner spans. There is nothing for trunking of 300 mm² or less. And there is nothing at all for the fire condition.

Checklist: reading the spacing tables

Banded the cable on its overall diameter — and a flat cable on its major axis.Table D1 note
Used the manufacturer’s figure above 40 mm overall diameter rather than continuing the last row.Table D1 note
Applied the horizontal spacings to every run more than 30° from the vertical.Table D1 note
Kept the units straight: clips in millimetres, conduit and trunking in metres.Tables D1, D3, D4
Placed a support within 300 mm of every bend and fitting.Tables D3, D4 note (b)
Kept the inner radius of every conduit bend at 2.5 times the outside diameter or more.Table D3 note (c)
Kept flexible conduit short enough that it needs no support along its run.Table D3 note (b)
Followed the manufacturer, not Table D4, for lighting suspension trunking and where strengthening couplers are used.Table D4 note (b)
Checked the tabulated spacing assumes maximum permitted cable fill and no other mechanical stress.Tables D3, D4 note (a)

Before the spacing: choosing the system

A spacing answers a question that only makes sense once the system is chosen, and Section 8 spends most of its length on that choice. Four product standards cover the ground — BS EN 61537 for tray and ladder, the BS EN 50085 series for trunking and ducting, BS EN 61386 for conduit, BS EN 61534 for powertrack — and naming the one you are buying to is the difference between a specification and a preference.

Trunking and ducting are not the same product. A trunking system is an enclosure for laying cables in; a ducting system is one for drawing cables through. Ducting is non-openable and trunking has a lid of some type. That decides how the cables get in, and whether they can ever be replaced without opening the building fabric.

Two details here are cheap to specify and expensive to retrofit. Vertical trunking wants cable support pins, threaded through so the weight of a riser does not settle onto the insulation in one place. Horizontal trunking wants clips or retainers, so the cables stay put when someone takes the lid off. And flexible or braided conduit is not a protective conductor — it cannot be terminated reliably enough and any break compromises it — so a separate CPC goes inside and is terminated at both ends.

Checklist: choosing the system

Materials, corrosion and external influences

Steel containment is chosen by its finish more often than by its section, and the finish is an environmental decision. Where dissimilar metals meet, the difference in their electrochemical potential drives the corrosion between them: BEAMA's best practice guide for ladder and tray holds that difference to 300 mV externally and in marine locations, and 500 mV internally. Specify a corrosion resistance class rather than the word “galvanised”, which covers finishes that behave very differently.

Cutting hot dip galvanised steel on site removes the protection at the cut. Tray, basket and trunking are all cut, drilled and de-burred during installation, and the exposed steel has to be made good with a zinc-rich cold galvanising compound. It is one line in a specification and an hour on site, and it is where external containment usually begins to fail.

Two cases catch people out. Zinc whiskers — conductive crystals that grow slowly and unpredictably out of zinc-coated surfaces — are widely acknowledged, and the risk is accepted as very small: there are no reported instances of equipment failure attributed to whiskers on containment. But in data centres and server rooms, where they have been suggested as a cause of malfunction, stainless steel, coated mild steel, PVC or GRP avoid them altogether. And non-metallic containment gives no electromagnetic screening at all, for its contents or for its surroundings — a real loss where power and data share a route, and the reason conductive spray coatings exist for PVC trunking.

Checklist: materials, corrosion and external influences

The spacing is an input, not an answer

A support spacing is a number that decides a load. Everything above the cable hangs off it: clip, containment, channel, drop rod, nut, anchor — and the chain is only as strong as the worst link at the condition you are checking.

The arithmetic is not difficult. Take the weight per metre of the containment and the cables it carries, multiply by the spacing, and you have the load at one support. Multiply by g for a force and apply your partial factor. That is the whole build-up, and the only term the designer controls freely is the spacing.

A chain of boxes joined by arrows showing containment weight in kilograms per metre multiplied by the support spacing in metres to give the load at one support in kilograms and then a factored force in newtons, with two panels below giving the smallest drop rod that carries that force at two hours under BS 8519:2010 and under BS EN 1366-5. — The load build-up is nothing but multiplication, and the spacing is the only term the designer controls. The rod size at the end of it depends on which published stress set you are working to.

Section 8.4.4 lists seven things that go into that calculation, and only the first is the weight. The others are the ones that get skipped: how the load is distributed rather than how much of it there is, how the bracket is actually secured, what the structural engineer will allow that building element to carry, and whether the route crosses a protected escape route — which changes the fire duty rather than the arithmetic.

Checklist: the load calculation

Dead weight is not the only load. Section 8.4.3 lists seven further forces the bracket and its fixings may see, and none of them appears in a weight calculation. Pulling a heavy armoured main in imposes a force during installation that the finished system never sees again. External runs get wind and snow. Containment expands and contracts. And single-core cables under fault throw the electromechanical forces that cleat spacing exists to resist.

Checklist: the forces beyond dead weight

Installation forces — pulling heavy armoured mains and submains in.Section 8.4.3(5a)
Wind loading, where the containment is external.Section 8.4.3(5b)
Snow loading and build-up, where the containment is external.Section 8.4.3(5c)
Expansion and contraction of the containment with temperature.Section 8.4.3(5d)
Vibration, and its effect on the support and fixing over time.Section 8.4.3(5e)
Seismic forces, in areas where seismic activity is common.Section 8.4.3(5f)
Electromechanical forces transferred by single-core cables under fault conditions.Section 8.4.3(5g)

Which is exactly why the fire case is not simply “the same design, closer together”. The load is linear in the spacing. Halve the spacing and you halve the load. But what is holding it has not lost half its capacity — it has lost far more.

What each link keeps when the fire starts

Steel does not fail in a fire so much as go soft. A support channel tested to a fire rating keeps roughly three quarters of its ambient strength at 30 minutes, two fifths at 60 minutes, and about a fifth at 120 minutes. The channel nut behaves similarly — its slip load drops to around a fifth. Those are large reductions, but they are survivable ones: a fifth of a strong section is still a section.

Here is the trap. The drop rod falls further. At ambient a threaded steel rod is worked at something like 100 N/mm². In fire it is allowed a small fraction of that, and there are two published sets of numbers, which do not agree.

A grouped bar chart of allowable tensile stress in newtons per square millimetre at ambient, thirty, sixty and one hundred and twenty minutes for two published sets. Both start at one hundred at ambient. BS 8519:2010 falls to thirty, fifteen and ten, and BS EN 1366-5 falls to nine, nine and six. — Both sets start from the same ambient stress and end a factor of ten to seventeen below it. The gap between them is why a rod sized some years ago may not be the rod you would specify today.

Maximum allowable tensile stress in a steel drop rod, N/mm²
Set	Ambient	30 min	60 min	120 min
BS 8519:2010	100	30	15	10
BS EN 1366-5	100	9	9	6

BS 8519:2010 gave the upper row. BS EN 1366-5 gives the lower one, and the IET guidance records that BS 8519 was under review and likely to adopt the more onerous figures.

The consequence is worth stating plainly. A design sized on 10 N/mm² at two hours has a rod working at 1.67 times the stress that 6 N/mm² permits. That is not a rounding difference; on a real bracket it is the difference between one rod size and the next, or between two sizes. If you are reviewing an existing installation, the first question is not whether the calculation was done — it is which set it was done against.

The rod loses more than the channel at every duration. Because the load falls only in proportion to the spacing, closing the brackets cannot recover a rod that has lost an order of magnitude.

Put the two together and the article's point falls out as an inequality: at every fire duration, the rod retains a smaller share of its ambient capacity than the channel does. At two hours the channel is at about 20 per cent of its strength and the rod at 6 per cent. The rod governs, and because the load only scales with the spacing, you cannot bracket your way out of it. The answer is a bigger rod, a fire-tested channel and an anchor qualified for the condition.

One subtlety that catches people comparing capacities. A channel's ambient rating is frequently limited by deflection rather than strength, and deflection is a serviceability limit that nobody checks during a fire. So the fire-tested capacity is a fixed fraction of the ambient strength column, not of the lower number you were actually allowed to hang on it. Compare like with like, or the channel will look worse than it is and the rod better than it is.

Checklist: the fire condition

Recorded which published stress set the drop rods were sized against.BS 8519 / BS EN 1366-5
Checked the rod at the fire condition and not only at ambient.Section 8.4.5
Taken the channel capacity from fire-tested data rather than the ambient table.Section 8.4.6
Derated the channel nut for the fire condition.Section 8.4.6
Qualified the anchor for the fire condition and for the substrate it is going into.Section 8.4.3(6)
Given the support system a fire survival time at least equal to that of the cables it carries.Section 8.4.3(1)
Confirmed circuit integrity is not reduced below that afforded by the cables, for emergency lighting, fire detection and life safety circuits.BS 5266-1, BS 5839-1, BS 8519
Sought specialist advice where a beam or channel has to perform under fire conditions.Section 8.4.6

A worked span

Take a 300 mm cable ladder carrying a normal power load, on trapeze brackets at 1.5 m centres. Loaded, that is around 36 kg for every metre of run, so each bracket carries roughly 54 kg — call it 690 N once a partial factor is applied. At ambient that is a trivial load for an M10 rod, which is why nobody thinks about it.

Now ask for two hours. On BS 8519:2010's 10 N/mm² the smallest rod that carries it is M12. On BS EN 1366-5's 6 N/mm² it is M16. Same ladder, same cables, same spacing, same bracket — two rod sizes apart, entirely because of which document was on the desk.

And note what closing the spacing does. Going from 1.5 m to 0.75 m halves the load, which recovers roughly one rod size. Going from ambient to two hours costs you between ten and seventeen. The spacing is a real lever and it is nowhere near a big enough one on its own.

IP and IK: two ratings, and they are independent

An IP rating classifies protection against solid objects and against water. An IK rating classifies protection against mechanical impact, on an eleven-step scale from IK00 to IK10, where IK10 is 20 joules. They are separate systems and a high value in one implies nothing about the other.

The IP digits are not a matter of taste. BS 7671 classifies external influences in Appendix 5 — AD codes for the presence of water, AE codes for solid bodies — and each classification maps onto the IP rating the equipment needs. AD3, water falling as spray up to 60° from vertical, calls for IPX3. AE3, very small objects, calls for IP4X. Working from the external influence rather than from habit is what makes the rating defensible.

Two IP values turn up in this subject specifically. Single-core non-sheathed cables must be enclosed to at least IP4X or IPXXD — and note that for the IPXXD test, “access” means contact with any hazardous live part inside, not merely entry to the enclosure. And a conduit, trunking or ducting system may avoid internal fire sealing only if it is non-flame propagating, has an internal cross-sectional area no greater than 710 mm², and satisfies IP33. It is easy to fabricate a bend or a tee on site and lose the rating the rest of the run was specified to.

Checklist: IP and IK

Stated an IP rating for the containment and for the terminations into it.Section 8.9
Chosen the IP digits from the external influence codes rather than by habit.BS 7671 Appendix 5, Section 8.9
Checked that the glands and installation method actually deliver the claimed IP rating.Section 8.9
Stated an IK rating where impact protection matters, noting that IK is independent of IP.Section 8.8
Maintained the IP rating across any bend, tee or joint fabricated on site rather than bought in.Section 8.2.3

What goes on the drawing

None of the above survives contact with a site unless it is written down somewhere a installer will see it. “Clips at 300 mm horizontal, On-Site Guide Table D1” is a specification; “clip as required” puts the decision on whoever is holding the drill. The support detail for a 120-minute circuit is a different detail, not the same one with a note against it.

Checklist: what goes on the drawing

Stated the spacing and its basis — “clips at 300 mm horizontal, On-Site Guide Table D1”, not “clip as required”.Section 8.5
Marked the fire-rated runs and their durations on the layout, not only in a schedule.Section 8.4.2
Named the stress set the rods were sized on, on the calculation sheet.BS 8519 / BS EN 1366-5
Shown the whole chain checked — channel, nut, anchor — and not the rod alone.Section 8.4.3
Quoted the manufacturer’s curve and the span read off it for tray, ladder and basket, and said whether it is an end span or an inner one.BS EN 61537, Section 8.4.7

The containment size itself is the other half of this problem, and it is worth doing first: how much fits, and therefore how much it weighs, is what sets the load your supports carry. That is covered in containment fill and the 45% space factor. Where the run has to survive a fire, the duty holders and the scope are set out in BS 8519 fire-rated containment supports. And where single-core cables carry serious fault current, the fixing spacing is a force calculation rather than a table — see cable cleat spacing and short-circuit forces.

Sizing a real support system? The MEP bracket calculator takes the load through channel, rod, nut and anchor at ambient and at each fire rating, and the containment fill calculator tells you what the containment is carrying in the first place.

Frequently Asked Questions

How far apart should cable clips be?

It depends on the cable's overall diameter, whether the run is horizontal or vertical, and what kind of cable it is. On-Site Guide Table D1 gives four diameter bands. For ordinary non-armoured thermosetting or PVC sheathed cable the horizontal spacings run 250, 300, 350 and 400 mm as the diameter climbs from 9 mm to 40 mm, and the vertical spacings 400, 400, 450 and 550 mm. Armoured cable is not tabulated below 9 mm and goes wider above it — 350 to 450 mm horizontal. Mineral insulated and aluminium sheathed cable is much wider again, up to 1,500 mm horizontal, and is not tabulated above 20 mm. Above 40 mm overall diameter the table stops and it is the manufacturer's figure.

Do the Appendix D tables satisfy Regulation 521.10.202?

No, and the IET says so directly. The guidance notes that the tabulated spacings "provide examples that will meet the requirements of Chapter 52 of BS 7671 and not the specific requirements of Regulation 521.10.202". Chapter 52 is the weight and mechanical duty; 521.10.202 is the fire duty — the wiring system must not be liable to premature collapse in the event of fire. They are two questions and Appendix D answers one of them. On a job with fire-rated circuits you will end up with two spacings, and the fire one is shorter.

Does Regulation 521.10.202 apply to data and fibre cables?

Yes. It applies to all wiring systems without exception, and the IET guidance calls out metallic telephony and small-core fibre specifically, because they may have a low melting point. A plastic-clipped data run over an escape route is exactly the case the regulation was written for: the cable itself is no danger, but a curtain of dropped cable across a corridor is. Cables installed in or on steel containment systems are deemed to meet the regulation.

Which column applies to a sloping run — horizontal or vertical?

Horizontal, for most slopes. The note under Table D1 says the horizontal spacings may be applied to runs at more than 30 degrees from the vertical, and the vertical spacings apply only at 30 degrees or less from the vertical. So a 45 degree run takes the horizontal figure, which is the tighter of the two. It is easy to read it the other way round and end up with clips too far apart on a rake.

How do I measure a flat cable for the table?

On its major axis. Twin and earth is banded by its wide dimension, not by an equivalent round diameter and not by the thin one. It is the same convention the containment fill calculation uses when it takes the effective cross-sectional area of a non-circular cable as a circle of diameter equal to the major axis.

What spacing do cable tray, ladder and basket need?

Appendix D does not tabulate them. Open containment is supported at whatever span its published safe working load and deflection curves permit for the load it is carrying, tested to BS EN 61537, and that is a manufacturer figure rather than a regulation table. The end span of a run deflects more than the inner spans and is the one the curves are usually drawn for. Cleats are different again: their spacing is set by the peak short-circuit force, which is a calculation to BS EN 61914 rather than a lookup.

How much closer do supports go in a fire condition?

Closer is rarely the answer on its own. The load at a bracket falls in direct proportion to the spacing, but the capacity of what is holding it falls much further. A fire-tested support channel keeps roughly three quarters of its ambient strength at 30 minutes, two fifths at 60 and about a fifth at 120. A steel drop rod is allowed only 6 to 10 per cent of its ambient working stress at two hours, depending on which published set you are working to. Halving the spacing halves the load; the rod has lost an order of magnitude more than that. The fix is usually a bigger rod and a fire-tested channel, not simply more brackets.

Which allowable stress should I use for a drop rod in fire?

There are two published sets and they do not agree. BS 8519:2010 gave 30, 15 and 10 N/mm² at half an hour, one hour and two hours. BS EN 1366-5 gives 9, 9 and 6 — substantially more onerous — and the IET guidance records that BS 8519 was under review and expected to adopt the lower figures. Anything designed on the older set carries a rod between one and a half and three times more highly stressed than the newer one allows. If you are checking an existing design, find out which set it was sized on before you decide whether it is adequate.

Is the anchor or the rod the weak link?

Often neither on paper and both in practice. The chain is clip, containment, channel, drop rod, nut and anchor, and it is only as strong as the worst of them at the condition being checked. The nut is easy to forget and drops to about a fifth of its ambient slip load in fire; the anchor depends on a substrate whose specification is frequently unknown in an existing building, which is why physical tests get called for. Check every link at the fire condition, not just the one you sized first.

Sources and verification. The duty is BS 7671:2018+A4:2026 Regulations 521.10.202, 522.8.4 and 522.8.5 — none of which tabulates a spacing. The spacing tables are IET On-Site Guide Appendix D, Tables D1, D3 and D4, transcribed here from their reproduction as Tables 8.5, 8.6 and 8.7 of the IET Guide to Cables and Cable Management, which reproduces the On-Site Guide to BS 7671:2018 — verify against the current amendment before relying on them. The drop rod stress sets are that guide's Tables 8.2 and 8.3, giving BS 8519:2010 and BS EN 1366-5:2010 respectively; neither standard is held here and neither is quoted or summarised. Channel, rod, nut and anchor capacities are the indicative manufacturer data used by the MEP bracket calculator, and containment and cable weights the indicative catalogue data used by the containment fill calculator. Open containment spans are tested to BS EN 61537 and cleat spacing to BS EN 61914; both are named, not reproduced. All values are indicative and for illustration — verify against the current standards, the manufacturer's data and the project specification before use.