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Topic Title: Contactum CP boards - Big Bang
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Created On: 24 October 2008 07:57 PM
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 24 October 2008 07:57 PM
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slittle

Posts: 3582
Joined: 22 November 2007

Had a nasty today with a contactum CP board.

We've fitted contactum boards for years, never had a problem with them. This was the first CP board fitted.

Fitted board, done all the dead tests, all ok. re-energised and checked polarity on incoming side of main switch (ok) then energised board.

17th edition board so next move was to turn on RCD's one at a time. switched first one. Big bang and flash.

Having removed covers, there was an awful lot of molten debris on the inside of the busbar cover and up the back of the board.

1st RCD appears to have been dead short between phase and neutral on it's outgoing terminals resulting in it taking out the 63amp hrc fuse supplying it.

I'm 99 percent certain that it was not a whisker from the tri-rated interconnection cables shorting against the busbar.

The RCD in question is on it way back to the wholesalers to be returned to contactum.

May I suggest (as I didn't) that dead testing includes checking busbars to netural on these boards. Not a test we normally do but......



Stu
 24 October 2008 08:02 PM
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AMN

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I had a new Wylex split load board supplied to me a couple of years ago that had the busbar connected across the L and N terminals. Fortunately I noticed before energising.

AMN
 24 October 2008 10:08 PM
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napitprofessional

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The latest `flexi` dual rcd Wylex boards come with three busbars in a bag - so if there are any problems upon energization guess who`s to blame.

-------------------------
B. Eng (Hons) MIET
 24 October 2008 10:45 PM
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stateit

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Only time I've seen this is (heard, actually - I was in different room) is when apprentice had connected busbar across neutral as well as lives.

Just what's needed at end of afternoon and there's no big BS1361s in the van.

Yep, individual circuit dead tests won't actually find this fault, but a whole system dead test will!

-------------------------
S George
http://www.sg-electrical.com
 24 October 2008 10:54 PM
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alancapon

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The old style MG Isobar three-phase boards do it quite well too. A metal plate had to be inserted into the busbar, for the cb to connect on to. Under some circumstances, these could go into the busbar enclosure, sitting on one of the bars, then spin round and end up phase-to-phase if the board was knocked. They also have the element of surprise, as you never know whether a previous electrician has lost one inside. The bang and the busbar enclosure lighting up bright blue is spectacular.


Regards,

Alan.
 25 October 2008 12:39 AM
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truss

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We've just powered up a job - 12 bedsits - all Contactum CP baords, each with main incomer & 5no RCBOs. Out of 60 RCBOs installed, 2 of the 6amp ones went bang when doing the X5 RCD tests. It's the 1st time we've used the CP boards, to be honest the £18.50 per RCBO is what swung it.

As an aside these RCBOs don't come with a functional earth flying lead.

I think Contactum have changed manufacturer since the new CP range has come out. The RCBOs are made in China even though most of their gear is marked "Contactum England".

Not sure if i'll use them again.

Regards,

Trussy
 25 October 2008 04:22 PM
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stureid

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I've never installed contactum but have always thought they looked a bit naff with the split visor and the different coloured MCBs. Based on what I've read here, I'll be staying away from them.

I tend to use MK or Wylex as a matter of course just because you can pick them up pretty much anywhere.

-------------------------
Regards
Stuart

http://www.redelectrical.co.uk
http://www.redrenewables.co.uk
 25 October 2008 06:46 PM
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slittle

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The previous versions with the mcb's the same colour seemed ok. other than the plastic boards tended to flex a bit if the wall wasn't flat and could be tricky to put the lid on.

I think we'll be changing in the near future when I've discussed discounts at the wholesalers for other makes....

Stu
 25 October 2008 06:48 PM
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Zs

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Just lost this so re typing and it might come up twice.

Slittle, I had this myself this week on that job for the depressed chinaman so in a perverse way I am glad to see this thread.

I used a contactum 17th split because there was not enough room for my favourite hager. I had cut the bus bars myself, probably badly, and it arced across to the neutral under the RCD. Major bang. The inside of the bus bar cover took some cleaning, all sorts of little spatters in the board, and I was glad to have been wearing my plain specs that I had made recently and that I make a point of looking away on switching.

Made a note to stupid self to cut bus bars to within a millimeter of their life in future. Kindof glad to see yours.

Zs

Edited dire spelling. Fingers faster than brain.

Edited: 25 October 2008 at 07:06 PM by Zs
 25 October 2008 07:06 PM
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bakey1959

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Am I missing something, because I'm wondering why during the the 'dead' testing this wasn't identified.
 25 October 2008 07:22 PM
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Zs

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Woah Bakey, perhaps dead testing isn't conclusive? (like the earthing and bonding knowledge which changes the regs every time the regs are ammended and one day will be fully understood?). There's no denying the bang I heard when I switched that board on. It was a fault find. It was tested off the planet for days. 50p that says the rest of the posters on this thread do their testing conscientiously too.

Here are several of us saying about the same thing. Yes, I met the contactum guys a while back and it is a new factory in China.

Zs
 25 October 2008 08:37 PM
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slittle

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Zs,

Mine was a metal clad 8 outgoing board and the busbars came pre-cut so it only leaves whiskers from the tri-rated or a fault in the RCD.
I have to admit to energising the board with the front cover still off, but thankfully the plastic busbar cover in place, otherwise judging by the debris that it caught I could have been looking at a trip to the local burns unit.. (back to the earlier threads about arc protection !)
Ze was about 0.02 as the unit was pretty close to the sub on site so plenty of PSCC to make a bang before the fuse let go.
Covers on and long stick for the next ones.


Bakey,
I always,always check L-N at the mainswitch before re-energising, but to be fair the RCD's were both switched off at this point, equally IR L-N on the outgoing circuits was ok.
How many check L-N between the outgoing terminals of the RCD's ?? - clearly something I will be doing in future.


Stu
 25 October 2008 08:53 PM
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RRichard

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Originally posted by: truss

We've just powered up a job - 12 bedsits - all Contactum CP baords, each with main incomer & 5no RCBOs. Out of 60 RCBOs installed, 2 of the 6amp ones went bang when doing the X5 RCD tests. It's the 1st time we've used the CP boards, to be honest the £18.50 per RCBO is what swung it.

As an aside these RCBOs don't come with a functional earth flying lead.



I think Contactum have changed manufacturer since the new CP range has come out. The RCBOs are made in China even though most of their gear is marked "Contactum England".



Not sure if i'll use them again.



Regards,



Trussy





Edited: 25 October 2008 at 08:54 PM by RRichard
 25 October 2008 09:00 PM
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RRichard

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Purely because of price we have just tried a couple of CPN boards from BDC. I think they may be Chint ? Anyhow, i was pleasently surprised. Seem well made with loads of info, full sticker sheet and quite robust. RCBO's are £16.50 if you buy 5+, 3+3 split load board, £36. BDC advertised in the NICEIC mag this month, but like usuall they got all the pics mixed up in the add and showed a breaker at £16.50 along with a few other mistakes.
 26 October 2008 07:16 AM
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GeoffBlackwell

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Originally posted by: slittle
Ze was about 0.02 as the unit was pretty close to the sub on site so plenty of PSCC to make a bang before the fuse let go.







An alarm bell is ringing here .

I don't know what type of installation you are describing, but if Ze really is around 0.02 ohms, you would have a PFC of around 11.5 kA at 230 volts. Now the measurement of such low values of Ze with a loop impedance tester is so prone to error that it is generally a waste of time, however, if you have determined it by other means, are you sure that the CU has a high enough fault rating?

A consumer unit (more correctly called a Customer Distribution Board in the standard) to BS EN 60439-3 can have a conditional fault rating of 16 kA regardless of the rating of its mcbs etc. This is because the UK has an A-deviation to the European standard. This is described in Annex ZA of BS EN 60439-3.

The main point here is that it is based on the supply fuse being a BS 1361 fuse rated at 100A (a cut-out fuse). Such a unit will not have this conditional fault rating if a different (generally larger or of a different type) overcurrent device is used to protect it. If it is not set up like this its fault rating is likely to be very much lower because the protecting device let through energy may not be low enough to protect the unit.

So if your supply is not via a 100A BS 1361 fuse you may have a problem.

Now, there is more - one of the draw backs of this bit of UK trickery is that we end up with CUs that might suffer greater damage if a fault occurs in the unit itself. The A-deviation proves the CU by placing a fault 0.6 metres along the run of a final circuit and by including 3 metres of 16 mm² tails. If we have an overcurrent device in the range 32A to 40A, the final circuit must be 10 mm² cable. If you do some sums you will find that the actual fault current that flows during the tests is probably a good deal less than 9 kA - the exact value would depend on the temperature that the various cables reach during the test.

This all works - even for 1 kA rated BS 3036 fuses - because the BS 1361 fuse limits the let through energy.

A real fault within the unit might be worse than these tests predict and may, therefore, cause damage. The situation could become very much worse if the supply overcurrent device is not a BS 1361 100A fuse.

The moral of the story is comply with 512.1.2 and make sure you are using the equipment as intended - remember its only by a bit of UK 'magic' that CUs are allowed - like twin and earth, many of our EU partners would not want to use them .

Regards

Geoff Blackwell
 26 October 2008 10:15 AM
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slittle

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Geoff,

Agreed regaring low ze, the reading was based on what two different loop testers gave and the fact the sub is twenty yards away.

I'm reasonably happy with the design as it's only a small kitchen and toilet block in a unit, fed by a couple of meters of 25mm swa from a 100A MCCB in the metering room, which is fed from the DNO.

Fuse in my OP should have read 60A, not 63 but it had been a trying day. The units had cutout type fuse holders fitted in the past, I guess to provide demarkation as we control the intake/metering room and the underground SWA's, then it's up to the tenant who they use for their installations although the landlord does insist we get to look at it.

About to go for a week away with wifey and kids so will give it a bit of thought whilst watching the rain and

Stu

edited for spelling ...

Edited: 26 October 2008 at 10:18 AM by slittle
 26 October 2008 10:18 PM
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sparkingchip

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Six and a half years ago I went to fit a very fancy Kitchen in a very fancy barn conversion.

The builders Electrician had installed the Cooker Circuit but not connected it up, I needed to move the cooker switch a few inches, so I did this and as the Cooker Switch Socket had a neon (something I advoid) I insulation tested the two parts of the Circuit seperately, then put the Switch back into the Circuit and turned the power on without another L/N insulation test because of the neon, only carrying out L+N to E with the Switch in place, which I believe is all by the book.

The Switch exploded due to a internal L/N fault, being such a fancy job it was from a leading manufacturer, not a far eastern import.

Andy Betteridge.
 28 October 2008 08:34 PM
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kaichung

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On a related note, that is why I always place a 3amp DP switched fuse-connection unit, with neon, in line with all PIR outside light installations.

This way the chances of a megger test damaging the delicate PIR electronics will be minimised, as the neon will let some of the 500volts through itself, alerting the testing person to turn off the DP switched FCU before meggering it again...
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