Discuss Enclosure For Rcd To Protect A Tt System, Have I Got This Right? in the Electrical Forum area at ElectriciansForums.net

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Mattja

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Having a hard time figuring this one out, think I've got it but I figure best check with you guys!

On a TT system, metal CU so needs to be protected by a time-delayed RCD in the tails (to allow smaller Amp RCDs on sections of the board to trip first), and this time-delayed RCD should be in it's own enclosure. So far so good.


Now here's the catch... P.S. I bet you all just said "ahhh yes, I know what he's about to say" to yourselves and you're probably right:

If it's in a metal enclosure then if the incoming line tail faults to the enclosure then that's unprotected and the enclosure becomes live without protection, so obviously I can't do that no matter what. So it needs to be an electrically insulated enclosure, but do the 17th edition requirements for consumer units apply to this enclosure, being fire rated in particular? If so what do you recommend I use?
 
I believe the recommendation is to ensure that the wiring does not pose a significant risk of being able to short to the enclosure.
I.e the use of cable glands on entry and a direct run of the incoming tails into the RCD and cable clamps to retain the tails in place in case of inadvertent release of the tails from the terminals.
Though before the change in the regulations to require non combustible enclosures the use of a metal enclosure was considered far too dangerous!
 
Adequately support the tails, use a purpose made nylon tail gland, use a clamp if manufacturer makes one and change the main switch for a 100mA time delayed RCD to provide fault protection to the links between RCD's...Jobs a goodun.
 
Alright thanks guys. :thumbsup:

@lee unfortunately I cannot have them run direct into the CU and straight into the main switch as I'm very limited by the length of the tails the DNO has left me to work with and the position of the CU above the meter, so at the least I have to make a connection before the CU which may as well be my RCD. Cheers for the idea

So put the tails through nylon glands on entry and clamp them in place so they just cannot move? Sounds like the people setting the regs got fed up scratching their heads and said "sod it", but oh well I guess so.
 
Nice thought Taylor, those seal fairies are proper nice fellas dealing with those pesky fuse seals. Someone may not be so impressed if they were playing with the meter though, maybe I'm just paranoid.

Cheers for the suggestions Lee and Richard, will look those up but time I got some sleep now, goodnight all!
 
Chint! OMG, has the world come to this. One of the Caravanning clubs used to use their stuff and I'd find more inoperative than working.
 
Alright thanks guys. :thumbsup:

@lee unfortunately I cannot have them run direct into the CU and straight into the main switch as I'm very limited by the length of the tails the DNO has left me to work with and the position of the CU above the meter, so at the least I have to make a connection before the CU which may as well be my RCD. Cheers for the idea

So put the tails through nylon glands on entry and clamp them in place so they just cannot move? Sounds like the people setting the regs got fed up scratching their heads and said "sod it", but oh well I guess so.

Mattja are you saying the DNO left you tails on the consumer side and these are too short?
 
Europa components make and supply to wholesalers (but do not list on their website) the MEC2M which is a two module AMD3 enclosure.

Have you got a link to this enclosure Richard? I can find this enclosure http://www.rmdist.com/shop/view/-1335 which looks like the one you are talking about but it is open fronted so would not be Amd 3?
 
Have you got a link to this enclosure Richard? I can find this enclosure http://www.rmdist.com/shop/view/-1335 which looks like the one you are talking about but it is open fronted so would not be Amd 3?
I have not got a link as they do not advertise it on their website so it took a lot of effort to track down. It is the same as your link but with a metal lid fixed over the front. If you ask for an MEC2M from Europa components to be ordered for you at your wholesaler they should be able to get one (if they have a Europa account)
Enclosure For Rcd To Protect A Tt System, Have I Got This Right? MEC2Ms - EletriciansForums.net
 
Mattja are you saying the DNO left you tails on the consumer side and these are too short?
Well either them or whoever fitted the old CU, the tails just don't have enough slack in them to be brought in straight from the top of the CU. And I cannot relocate the CU to a lower position because the gas meter is in the way, not to mention the majority of the cables going out the back straight into a cavity wall and then upwards, so even if there was space for the CU lower down it would mean either running a load of new cables up through the wall or making a pigs mess of connectors and then sealing up a big hole in the cavity over them (basically either a mess or making the job too big, the idea having been to just improve the earthing).

Hence why I want to put an RCD in a smaller enclosure, there's just room for that lower down without getting too close to the gas, so I can simultaneously get the whole system on a time delayed RCD and extend the tails.

Thanks for the component suggestions, I spent a while looking around and matched up a suitable 4 module wylex enclosure (coming with a main switch a 2 modules free) with one of their time delayed 2-pole RCDs (had to get them from separate places but that's how the hunt goes I guess). A little more cost than I wanted, but now they've got an isolator switch (other then using the RCD for that) too. :)

Thinking I'll connect this enclosure straight to the MET with the same 10mm^2 I used for the water & gas bonding, so if the line somehow ever did fault to the enclosure at least it won't all go through whoever touches it!
 
Chint! OMG, has the world come to this. One of the Caravanning clubs used to use their stuff and I'd find more inoperative than working.
Yeah its carp gear but at the end of the day its only an enclosure. When I first started looking for 2-3 way amendment 3 enclosures to house and RCD they were as rare as rocking horse shyte and most manufacturers the smallest they made was 5 modules.
 

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