Enclosure For Rcd To Protect A Tt System, Have I Got This Right?

[Mattja]

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?

 

[Richard Burns]

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!

 

[Leesparkykent]

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.

 

[Mattja]

Alright thanks guys.

@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.

 

[Taylortwocities]

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,

Maybe the magic seal fairy will allow you to make those tails long enough to suit your purposes?

 

[Leesparkykent]

Chint make an amendment 3 compliant enclosure. Its 3 way so you would need 1 blank.

 

[Richard Burns]

Europa components make and supply to wholesalers (but do not list on their website) the MEC2M which is a two module AMD3 enclosure.

 

[Mattja]

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!

 

[richy3333]

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.

 

[richy3333]

Alright thanks guys.

@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?