Metal Trunking as CPC but how to make a hidden joint?

[santidreamer]

I am designing a hotel, rooms along corridors will be fed from steel trunking connected to PVC conduit into consumer units in each room. The corridor ceilings will be closed denying access to the trunking after installation.

I would like to use the trunking as the CPC but how do I connect the cables in the trunking so they conform to regultions? (No hidden joints or terminations).

When is a joint not a joint, when it is crimped soldered, brazered or welded.

Copper does not weld to steel so that leaves crimping.

Is a pop rivet a form of crimp? Can I rivet an eye crimp to the trunking?

Any better ideas on how to comply?

Steel trunking when installed correctly is an excellent CPC, seems a shame and waste of oney not to use it.

 

[mogga]

WHY are you using trunking Hotels iv seen are Basket,tray with twe ,SWA feeding the C.U. at rooms some times 1c.u for 2 rooms depending on layout

 

[santidreamer]

It is actually a condotel that is privately owned holiday resort in Thailand. So can not share C.U. as each room has an electric bill

SWA is or its equivalent (WITHOUT STEEL ARMOUR) is relatively expensive, so have opted for PVC singles.

Furthest rooms are 45m from distribution board so will have volt drop problems if cable size is dropped below 16mm.

10mm SWA on tray is OK for design current.

my understanding is that tray can not be used as sole CPC but trunking can.

So for a little extra cost of trunking over tray 16mm singles can be used same price as 10mm SWA type cable. If only I can find a way of joining the CPC to trunking. (Although no such regs actually apply here).

 

[mogga]

twin n earth does away with using tray trunking as CPC

 

[santidreamer]

Twin n Earth on tray is a good idea for the next project, already bought the trunking and 16mm singles.

Initial steered away from Twin n Earth because through fear of rodents eating the cable, although it is not a big problem here and all ceiling are sealed.

 

[ian.settle1]

We can tell you what you can do in the UK but as you are in Thailand it depends on what regulations if any you need to comply with.

 

[Engineer54]

I am designing a hotel, rooms along corridors will be fed from steel trunking connected to PVC conduit into consumer units in each room. The corridor ceilings will be closed denying access to the trunking after installation.

I would like to use the trunking as the CPC but how do I connect the cables in the trunking so they conform to regultions? (No hidden joints or terminations).

When is a joint not a joint, when it is crimped soldered, brazered or welded.

Copper does not weld to steel so that leaves crimping.

Is a pop rivet a form of crimp? Can I rivet an eye crimp to the trunking?

Any better ideas on how to comply?

Steel trunking when installed correctly is an excellent CPC, seems a shame and waste of oney not to use it.

What your doing is by far, better than a cheap crap basket and T&E installation, what a bloody abortion in a multi dwelling installation!!!

If you want to go with eye crimps as your connection to the steel trunking, then the good old nut n bolt connection has been around longer than me, and has more than well proved it's worth!! lol!!

 

[Deleted member 26818]

You do realise, that you will have to run a CPC down the length of each PVC conduit drop?
To my mind, the amount of time you will waste, measuring, cutting, crimping, drilling and screwing nuts and bolts, you might just as well run in a separate CPC through the trunking, rather than faffing around.

 

[Knobhead]

Bloody hell I thought you were older than Whitworth!

View attachment 8604

I’d go with your idea E54 bolted connections will also bond the trunking along it’s entire length.

 

[santidreamer]

I have no regs to conform to installations out here are beyond awful, I actually thought my earth loop impedance meter was broken the earthing in this country is that bad.

I am designing and testing it, labour is real cheap Thai sparkys are a tenner a day, so half a reel of earth cable is proportional worth saving.

I want the electrics to be UK standards.

 

[pennywise]

Is steel conduit expensive too?, why not do the drops to the rooms in steel then you have your continuity.

 

[Engineer54]

Twin n Earth on tray is a good idea for the next project, already bought the trunking and 16mm singles.

Initial steered away from Twin n Earth because through fear of rodents eating the cable, although it is not a big problem here and all ceiling are sealed.

No, it's a bad idea!!! That's not much better than the local electricians would install!! I think it was Mogga that made the argument for this type of installation for commercial shop installations on the assumption that it would probably be ripped out before too long. If he had a case for that senerio, (which i don't think so) Then there is certainly no case whatsoever for this type of installation being installed in what is going to be a ''Permanent'' situation!!!

What do you mean, rat's are not a big problem in Thailand?? Some of the biggest rats i've ever seen were in Bangkok, the place was riddled with rat's mice and just about every other type of rodent and pests!!

There is virtually no such thing, to any rodents or other fauna, as a closed or sealed ceiling, they will get in anywhere, probably the same way you brought your installation into the sealed ceiling areas....

 

[santidreamer]

Normally PVC singles are run (no conduit) in open access loft spaces, private dwelling owned by westerns do not suffer from rats eating the cables where I live on Koh Samui.

Our building will be fire sealed so no access is possible above the ceilings, concrete beams concrete plank for floors. furthermore there will be little food for the rats to be had inside the rooms.

This is a PME TNC -S installation with 16mm singles supply connected to BS EN 60898 50A breaker connected to a C.U. with BS EN 61009 RCBO. containing BS EN 60898 MCBs.

There is no earth bonding to be done, pvc tube cold water supply no exposed metal.

There is a ring circuit on a 32A MCB, max Zs =1.5 Ohm

What is the min earth cable size required?

Both the Zs requirements and the energy let through calculation (sqr of If x If x t / k) can be satisfied with relatively small earth cables

4mm main earth cable will give ring circuit Zs of 0.5Ohms (If ring has 1.5mm CPC)