Contactum RCD's & TD RCD's

[jamie.aston]

Hello All,

Quick question. I need to replece my CU and do a full rewire. I have already bought the CU, 30mA RCD & MCB's (Contactum) but have now come to order the 100mA TD RCD (TT Supply) and learned that contactum don't do them. Would it be OK to split my split board using a conversion kit so that the 2 RCD's come off the Main Isolation Switch. This would mean that i could use a 100mA RCD for the Lights, cooker (no socket on cooker unit), Combi Boiler, etc. and the 30mA RCD for all sockets, bathroom lights and shower. I know i could put a seperate TD RCD between the meter and the CU but would prefer to keep this nice and neat in one CU. Am doing it myself and notifying as i intend to use this job later on in my portfolio for NIC registration. Will also be running submain for shed (16mm SWA) from a 63A MCB on the 100mA RCD side, will this interfere with my Florecent tubes in my shed?

Thanks
Jamie

 

[JohnD]

it is acceptable to use a 100mA RCD on the non-socket circuits.

The problem you might have is getting the two RCDs separate so that they do not trip at the same time. This is the advantage of the TD RCD as it lets the other one trip first when they are in series, and in this case the fault will be cleared before the TD one trips.

I know how to do what you want using a large CU with two busbars fed from the man switch, where each has a separate isolator or RCD. I don't know if you Contactum one works like that. I can show you a pic of a MEM double-decker that works that way if I haven't explained it.

An alternative method is to use a TD RCD as if it was a "main switch" in the tails between your meter and your CU or Henley. In this case you do not need a 100A DP Isolator.

p.s. it is preferable to run the submain for the shed off the non-RCD side, and have an RCD in the shed. Then when you are working in the shed and have a trip, you can reset it without tramping back into the house. Ulesss you have a TD RCD, they wil almost certainly both trip at the same time, otherwise

 

[RF Lighting]

Or take that CU back to the shop and buy one fit for purpose

 

[jamie.aston]

Sorry John i must not have been too clear. I would take tails from the Main Iso to both RCD's, this way the 2 RCD's won't be inline so i shouldn't have discrimination probs?

 

[JohnD]

Or take that CU back to the shop and buy one fit for purpose

better idea!

Sorry John i must not have been too clear. I would take tails from the Main Iso to both RCD's, this way the 2 RCD's won't be inline so i shouldn't have discrimination probs?

You would have to configure it like a dual-tariff CU and not as a Split-Load CU. Can you draw a picture of how you intend to do it? Your Contactum CU may not make this easy.

 

[jamie.aston]

Hello RF,

Only TD RCD's in TLC are MK, it would cost me MEGABUCKS to replace everything i've bought for an MK one. Plus i was under the impression that the method i had describes was an accepted one

Pic as Requested John

Thanks
Jamie

 

[RF Lighting]

Have you contacted the DNO to see if a PME upgade is available?

There is more than just one electrical wholesaler in the world.


CU £64.35


RCD £81.08


Total £145.43 for a decent quality CU, Main TD RCD, additional 30mA RCD, and 10 MCBs (and a free main switch for your tails if you like)

Hardly "MEGABUCKS"

 

[jamie.aston]

Already contacted DNO to ask for PME after looking on their website i was expecting (and happy) to pay around £49 + VAT but when i phoned they told me as it wasn't available in my area it would cast me around £300 as they would need to do work on their network. I think with all my MCBs, RCDs and CU the total was less than £150 but i will go back to TLC and ask them to price up replecements from MK.

 

[JohnD]

jamie.aston - yes, your diagram works if you can do it like that. The MEM unit I am thinking of is built to be used that way, and has a main switch in row one, feeding an RCD in row 1 and an independent RCD in row 2. Each RCD feeds a busbar of MCBs. The main switch can be an isolator or a TD RCD, or you can swap RCDs for isolators and vice-versa if you feel like it.

 

[jamie.aston]

Cheers John, think i will still go back to tlc and price up a replacement though. As you have both said, fit for purpose would be best.

On a sidenote i have a couple of pics of the current setup, anyone think it needs replecing?

Jamie[/img]

 

[Taylortwocities]

Jamie, its perfect like it is. Its been working like that for 40 years so it must be ok

 

[JohnD]

grrrrr, I hate electricians who use G&Y tape to stick things together that aren't earth wires.

25mm tails will be nice.
Can you junk the Henley?

 

[jamie.aston]

Part of the reason i'm doing a full rewire & changing out CU is to tidy things up and get rid of the henley (will have to do the same with the telephoney stuff there too, thats the stuff taped up in earthing insulation tape) but the main reason is for safety, the previous owner was a plasterer and while he's done a cracking job on the ceilings, walls and dashing he clearly wasn't comfortable (to say the least) with electrics. Only thing is now i'm gonna have to ruin my walls to chase out for cables and switches. Also if you look at the black box, the yellow and blue fuse carriers (20A & 10A i think) are wired in parallell, if you pull one of them the circuit stays live, you have to pull both to isolate.

jamie

 

[jamie.aston]

Hi Guys,

Just started pricing up a MK board and i don't think they make a split load unit for my needs. These are what i would need for a full rewire in my house.

30mA RCD = 2 Module
4 x 32A Ring Mains - 3 Floors + Kithchen = 3 Module
1 x 40A Radial - Shower = 1 Module
Edit: 1x 6A Radial - Bathroom Lights = 1 Module (17th Edition)
100mA TD RCD = 2 Module
1 x 50A Sub Main - Shed/Garden = 1 Module
1 x 40A Radial - Cooker = 1 Module
1 x 20A Radial - Combi Boiler = 1 Module
1 x 6A Radial - Fire/Carbon Monoxide Alarms = 1 Module
3 x 6A Radial - Lights = 3 Module
Main Isolation Switch = 2 Module

I would have to buy a 21 Way board and convert it to split load. Am trawling TLC now and trying to work it out.

Just finished working it all out. If i buy an extra 100mA RCD and fit it to my contactum board the total cost of the cu, rcds and mcbs will be £114.42 (inc VAT), if i change everything to MK and purchase 100mA TD RCD it will cost me £280.47. Looks like i will be sticking with contactum!

Jamie

 

[RF Lighting]

You pays your money you takes your chance


I'm looking to buy a new car. I've seen these two, which I can afford either one of.

Which do you think I should get?

1.

2.