Call out to an Overloaded board

[Robert cooke]

Was called out tonight to this beauty of a job. They’ve been having problems with they’re air source heat pumps, which are fed from a sub main.

Consequently, they have plugged in 7 x 2kw fan heaters to warm the house. Now, the sub main has been fed directly from the top of the rcd (see picture), no mcb to protect it. My thoughts tell me this is a big no no, but the guy will go for the jugular of the guy who fitted it all, so hopefully you will all either agree or disagree before I speak to him tomorrow ?

I need to look further, but I suspect that all the heaters are on circuits on the same rcd, so can we put that much of a catastrophe down to just overload? Surely it should of tripped? It took out the 100a dno before it stopped.

Cheers

 

[Strima]

Good job that's one of those new fangled metal boards that will stop fires... Oh, hang on a minute...

Whoever installed the sub-main with no overload protection needs a bit of a slap to start with. Basically the DNO fuse is protecting the sub-main.

Any certification???

The homeowner has now also learnt what happens when you plug a load of heaters in...

 

[Wilko]

Very ugly - lucky the service fuse melted before the whole lot cooked. To me, it does look like load related failure of the RCD, which I see is rated to 63A. Looking at the board, the circuits protected include immersion at 3kW and the socket circuits which I assume the 14kW worth of fan heaters were plugged into. If they were all on the load is about 71A, which may be enough to cause this, but it would not have melted the service fuse. Was there any load on that (incorrect) submain? Perhaps service fuse melted on SC fault as the RCD collapsed?

 

[PEG]

Lovely pics - the DNO once again,providing suitable discretion...

 

[Robert cooke]

Cheers for the replies! Yes the submain will have had load on it, 2 air source heat pumps which are about 20a peak each. There is also a breaker in the submain labelled immersion heater so potentially 53a on there.

As far as I know there is no certification for it all. The sub main will be getting changed tomorrow aswell, and il likely take it straight back to the service head on tails and keep it completely separate to the house board.

 

[Wilko]

That would account for it, perhaps twice the rated current through that RCD

 

[Gavin John Hyde]

It might be worth you keeping the melted rcd and various bits attached and sending it to the manufacturer. As a lot of the better makes such as schneider like to see the parts to both identify any falings but to look at improvements. A few years ago i know somebody who sent a damaged rcd and now melted breakers not so different to yours and got a box full of goodies back...
Either way the person who put the submain from the rcd like that has some explaining todo in my view? I hope hes got insurance! Might try to say it was the heaters that tipped it over the edge....

 

[PEG]

It might be worth you keeping the melted rcd and various bits attached and sending it to the manufacturer. As a lot of the better makes such as schneider like to see the parts to both identify any falings but to look at improvements. A few years ago i know somebody who sent a damaged rcd and now melted breakers not so different to yours and got a box full of goodies back...
Either way the person who put the submain from the rcd like that has some explaining todo in my view? I hope hes got insurance! Might try to say it was the heaters that tipped it over the edge....

So that he may be entitled to claim for the theft,of part of his design

 

[Toneyz]

I had to take a second look at the photo as never used one of these boards before as usually the supply to the RCD is at the top but in these boards, the supply looks as if it is in the bottom, therefore, the load of this unprotected sub main and the MCB loads are going through the RCD too much current.

 

[LeeH]

Wow, a proper DIY job or a Electrical Trainee wonder I presume. ‘Yeah that 63A breaker should do it’

I bet it absolutely pen and inked!

 

[Wilko]

(He) Might try to say it was the heaters that tipped it over the edge....

He might try, but for me the design was wrong. No protection for submain and too many heavy load circuits connected. Not "by the book" but 63A RCD likely to have been ok with the load of 70A from heaters and immersion. However the added load from the unprotected submain load meant it was now possible to grossly overload that RCD, as apparently happened .

 

[marconi]

Remember Ohmic heating is I squared R not IR so the heating effect increases very rapidly with increasing current.

I Isquared
1 1
2 4
4 16
8 64
16 256
32 1024
64 4096
80 6400

 

[Pete999]

Good job that's one of those new fangled metal boards that will stop fires... Oh, hang on a minute...

Whoever installed the sub-main with no overload protection needs a bit of a slap to start with. Basically the DNO fuse is protecting the sub-main.

Any certification???

The homeowner has now also learnt what happens when you plug a load of heaters in...

Any certification? of course not bloke that did that abortion was probably illiterate, what a mess, bet that stunk the place out, you mention heat pump install, probably another post wonder course installation, Crikey what have we unleashed with all these short courses? I'm biased I know, when it comes to training establishments.

 

[Pete999]

Remember Ohmic heating is I squared R not IR so the heating effect increases very rapidly with increasing current.

I Isquared
1 1
2 4
4 16
8 64
16 256
32 1024
64 4096
80 6400

Remember Ohmic heating is I squared R not IR so the heating effect increases very rapidly with increasing current.

I Isquared
1 1
2 4
4 16
8 64
16 256
32 1024
64 4096
80 6400

Thank you Mr Marconi, memories of sweating over calculations you are mentioning came flooding back to me.

 

[andyb]

Good job that's one of those new fangled metal boards that will stop fires... Oh, hang on a minute...

It probably did stop a fire Strima. It contained it in the enclosure, the board itself did not ignite.

 

[Gavin John Hyde]

We are all agreed uts a sh!t storm of a piece of work from whoever installed it. Given that it nearly caused a nightmare scenario i reckon building control and maybe even the police should know... Could be a rare case where somebody gets prosecuted?? Doubt they notified it!!
A nice story in local paper about cowboy electrician and how house nearly caught fire will motivate them into taking action.

 

[telectrix]

I had to take a second look at the photo as never used one of these boards before as usually the supply to the RCD is at the top but in these boards, the supply looks as if it is in the bottom, therefore, the load of this unprotected sub main and the MCB loads are going through the RCD too much current.

pretty sure the RCDs are incoming at top. tails come from bottom of main switch to |RCD top. then busbars bottom of RCDs to bottoms of MCBs. the weird thing with these boards id that the L and N on the main switch are reversed and the busbar has a crank in it to take L to the right.

 

[PEG]

We are all agreed uts a sh!t storm of a piece of work from whoever installed it. Given that it nearly caused a nightmare scenario i reckon building control and maybe even the police should know... Could be a rare case where somebody gets prosecuted?? Doubt they notified it!!
A nice story in local paper about cowboy electrician and how house nearly caught fire will motivate them into taking action.

Really? You didn't call them the other day,when Kentucky FC was shut,did you?

Get the appropriate scheme on it...and they can eventually email a firm missive,recommending that the culprit promises to think about maybe sitting his 2391...

 

[Strima]

Any certification? of course not bloke that did that abortion was probably illiterate, what a mess, bet that stunk the place out, you mention heat pump install, probably another post wonder course installation, Crikey what have we unleashed with all these short courses? I'm biased I know, when it comes to training establishments.

As a Electrical Trainee I completely agree...

It probably did stop a fire Strima. It contained it in the enclosure, the board itself did not ignite.

My comment was tongue in cheek, sarcasm doesn't come across very well on a forum.

 

[Wilko]

pretty sure the RCDs are incoming at top. tails come from bottom of main switch to |RCD top. then busbars bottom of RCDs to bottoms of MCBs. the weird thing with these boards id that the L and N on the main switch are reversed and the busbar has a crank in it to take L to the right.

Yes, that could be right. If so, then RCD didn't have the submain load through it (?). Also, it looks like L and N reversed on the RCD ...