How do I make this safer than it is now?

yellowvanman · Mar 13, 2012

TT system wired about 10 years ago, using a 16th Edition board but with no 100mA RCD as main switch. (muppet!)

As it stands the 30mA doesn't trip and so needs changing anyway.

Whats the best way to protect the non RCD circuits without spending a fortune? The options I think I have are:

1) Change main 100A switch for a 100mA time delayed RCD - as it should have been in the 1st place

2) Change main 100A switch with a 30mA RCD - trouble is there is no discrimination with the other RCD in the board! Or don't even bother changing the other RCD and just have 1 protecting all circuits!

3) Change non RCD MCBs with RCBOs - too expensive.

Anyone got another option? I'm inclined to do No. 2.

i=p/u · Mar 13, 2012

option 2 seems easiest

johnboy6083 · Mar 13, 2012

i would use option A. Then you have discrimination, and the option to add RCBO's later if the client wishes

WPD Lad · Mar 13, 2012

See if the DNO will give you a PME?

ezzzekiel · Mar 13, 2012

option 3 for me, cost shouldnt be an issue.

TPES · Mar 13, 2012

When I used a TT for my assessment there was no 100mA RCD as a main switch, there was a dual RCD CU with 30mA protection to every circuit.. This was perfectly acceptable

telectrix · Mar 13, 2012

buy a dual RCD board from B&Q £50. 10% off on wednesdays if you not over 60, take your granny with you.

ezzzekiel · Mar 13, 2012

TPES said:
When I used a TT for my assessment there was no 100mA RCD as a main switch, there was a dual RCD CU with 30mA protection to every circuit.. This was perfectly acceptable

If all circuits had 30ma protection then there would be no need for a 100ma, depending on the amount of non protected circuits then board swap as tel says sounds the better option

Amp David · Mar 13, 2012

What board is it by the way?

telectrix · Mar 13, 2012

BG, British General. 10 way, hi integrity.

yellowvanman · Mar 13, 2012

Legrand board.

I reckon changing MCBs to RCBOs would be cheaper than changing board but customer doesn't want to pay that sort of money. Its been like this for 9-10 years and obviously customer asks why do I need to spend money on this? I'm twisting her arm to do something at least.

Sorry I thought the question was directed at me.

Amp David · Mar 13, 2012

Only asking regards board make as depending on how many RCBOs you need it'll probably be cheaper than the time delayed RCD option.

Yes, sorry it was aimed at YellowVanMan.

Engineer54 · Mar 13, 2012

If this is your typical 200 ohm UK TT system, then it's got to be all RCBO, with a 100mA RCD front end!! .... As wirepuller says it'll not be too often, you'll get two RCD devices failing on you at the same time... lol!!

Knobhead · Mar 14, 2012

Engineer54 said:
As wirepuller says it'll not be too often, you'll get two RCD devices failing on you at the same time... lol!!

Famous last words.
I’ve just been watching a documentary about the Titanic!

Geordie Spark · Mar 14, 2012

Tony said:
Famous last words.
I’ve just been watching a documentary about the Titanic!

Damn !!!

I would have liked to watch that, but didn't know it was on.

Which channel was it on Tony?

Maybe it'll be repeated later.

yellowvanman · Mar 14, 2012

Engineer54 said:
If this is your typical 200 ohm UK TT system, then it's got to be all RCBO, with a 100mA RCD front end!! .... As wirepuller says it'll not be too often, you'll get two RCD devices failing on you at the same time... lol!!

Ze isn't that bad 13 ohms ish. Ideal situation would be to put RCD and RCBOs but in the real world some people can't afford it!

durhamspark · Mar 14, 2012

I had 1 similar to this recently although it was a tncs system.

The problem I had was that I had carried out alterations to a few of the circuits on the main switch side of a 16th ed split load board meaning I had to rcd protect them as the cables were buried in the plaster.

It was a tight board so rcbos simply would not fit. The way I saw it I had 2 options.

1. move mcbs across to rcd side and buy new busbar comb as the existing did not have enough spares

2. Replace main switch with 30mA rcd and as the links were flexible, feed the 2nd rcd from the supply side of the main one so they are not connected in series.
I was fortunate in this case as there was an isolator switch in the meter cabinet so I removed the "Main Switch - isolates all circuits " sticker and made a warning label stating "isolate at meter cabinet"

This may be an option for you to consider.

Engineer54 · Mar 14, 2012

yellowvanman said:
Ze isn't that bad 13 ohms ish. Ideal situation would be to put RCD and RCBOs but in the real world some people can't afford it!

That's Good to hear. Well there's certainly one thing you can do to improve this installation then, with an already existing Ra of 13 ohms.... lol!!!

telectrix · Mar 14, 2012

bang in a scaffold pole?

Engineer54 · Mar 14, 2012

telectrix said:
bang in a scaffold pole?

Haha!! ...Seen that done before too, as well as other bits of discarded pipework!!

yellowvanman · Mar 14, 2012

durhamspark said:
2. Replace main switch with 30mA rcd and as the links were flexible, feed the 2nd rcd from the supply side of the main one so they are not connected in series.
I was fortunate in this case as there was an isolator switch in the meter cabinet so I removed the "Main Switch - isolates all circuits " sticker and made a warning label stating "isolate at meter cabinet"

This may be an option for you to consider.

Yes I've seen that before but forgot all about it - thanks.