Electrical issue with AC consumer unit

[Trident]

Probably in the if you have to ask you know the answer but...

The CU on a boat I am working on has about 10 MCBs which have been wired with the live from the sockets etc in to each MCB and the neutral from the sockets to the bus bar. Earth also to busbar . Out of each MCB comes a neutral wire (pre wired) which can go to the busbar allowing the N wire from the sockets to go to the MCB as well rather than direct to the busbar - it has not been wired using these as I said.

All the blue N wires from the MCBs are just hanging there unconnected and unnecessary but I noticed the other day one was arcing occasionally which is clearly a safety issue if only for fire.

1) Is this an induced current from the live inside the MCB - if not what? If so does this inherently mean the MCB is faulty and should be replaced?
2) Is it best practice to re-wire this so that all N go in to the MCB and all MCB neutral out wires to the busbar?

Thanks

 

[rogerthebodger]

I take it that the MCB's you have are 2 pole. If so the neutral should go to the same device are the line

 

[davidpbo]

Check the writing on the MCB. If it has a current rating e.g. 5A, 16A etc. and another saying 30ma or similar then it is probably a combined MCB/RCCD.

It sounds like the MCBs are combined MCBs and RCCDs (Earth Leakage Breakers) if these were to be wired correctly the neutral wire attached to the MCB/RCCD goes to the neutral bus bar, the neutral from the sockets would go to the neutral terminal on the MCB/RCCD and the live to the live terminal of the MCB/RCCD.

If they are a single breaker width then they are probably single pole. I.e they only break the live connection. Double pole would break live and neutral.

RCCD stands for residual current circuit device. It trips the circuit if there is an imbalance of more than a set current, typically 30ma on a final circuit, between live and neutral. Consequently both L and N have to pass through the device for that to work.

It sounds like they have just been wired for overcurrent protection with just the live taken through them. I would be dubious about that as the device may not be being used in the way it was designed for.

At the very least get someone to have a look at if you don't feel 100% confident in what you are looking at and insulate any flying leads. Obviously disconnect from any mains supply whilst messing around with things.

 

[TernVI]

Does each MCB have one neutral or two?
If it has two then it's some sort of double pole breaker.
If it has one only could it be an illumated MCB (I saw some once!) ?
That would explain the behaviour, the blue wire would be at 'live potential' with no current drawn but would spark to earth with a current limitted by the bulb/neon/led circuit?

 

[PaulRainbow]

Rather than guessing and getting incorrect/dangerous advice, it would be best to post a picture or details from the device, or both.

That said, i suspect it's a single pole RCBO, if you look at the terminals they would be marked something like "L in"," L out" and "N out". If that's the case, the flying lead should be connected to the neutral busbar and the load to the device "N out"

 

[ianj99]

RCBO's also often have an earth wire, or at least the type I have for my EV charger does. L in and out, N out , blue wire for the N in and g/y earth. (it's single width version)
The earth is for testing it and there is a small button next to the lever. If there isn't a test button, its probably a dp mcb with Live + switched Neutral.

 

[prv]

I think the answer’s already been given - just observing that it’s bloody scary that someone who didn’t know the difference between an MCB and an RCBO would take it upon themselves to assemble a consumer unit...

Probably worth advising your customer to get the whole installation checked - whoever built that box may have done other work elsewhere on board.

Pete

 

[rogerthebodger]

As Paul says we don't really know if the unit is a MCB 2 pole or a RCBO which are mainly 2 pole any way.

Which ever way it is to have some loose wiring not connected to any thing does question the knowledge of the original supplier of the consumer unit.

I cannot see a consumer unit being fitted with 10 RCBO which is why a 2 pole MCB overload made more sense to me

2 pole MCB

RCBO

 

[pyrojames]

I think you need to get a professional to help. If you are working on someone else's boat without electrical qualifications, then you could be in serious trouble. If it is your boat, then ask advice, but it doesn't really seem that you know either what the units are or how they should be wired. Not something that you want to work out by trial and error.

 

[prv]

I think you need to get a professional to help. If you are working on someone else's boat without electrical qualifications, then you could be in serious trouble.

I assumed he was there to do some sort of non-electrical work and had noticed the consumer unit while going about his plumbing or varnishing or whatever.

Pete

 

[prv]

As Paul says we don't really know if the unit is a MCB 2 pole or a RCBO which are mainly 2 pole any way.
...
I cannot see a consumer unit being fitted with 10 RCBO which is why a 2 pole MCB overload made more sense to me

True we don’t know for sure without more detail, but units that resemble normal MCBs (enough for the OP to call them that) but with neutral pigtails hanging out of them, are very likely to be single-way RCBOs.

It’s a while since I paid any attention to the subject but I believe RCBOs on all circuits is not uncommon nowadays - it’s the next logical step from the “17th edition” split CUs with two RCDs and a gaggle of MCBs on each, mostly because of the cost of RCDs at the time. Ten circuits is a lot for most boats, of course, but if you have that many then the corresponding ten RCBOs isn’t so unusual as to be disbelieved.

Pete

 

[pyrojames]

I assumed he was there to do some sort of non-electrical work and had noticed the consumer unit while going about his plumbing or varnishing or whatever.

Pete

Maybe, but you wouldn't be looking at busbars and connections into breakers without opening up the consumer unit.

EDIT Unless the installation was truly appalling and dangerous!

 

[davidpbo]

As Paul says we don't really know if the unit is a MCB 2 pole or a RCBO which are mainly 2 pole any way.

Which ever way it is to have some loose wiring not connected to any thing does question the knowledge of the original supplier of the consumer unit.

I cannot see a consumer unit being fitted with 10 RCBO which is why a 2 pole MCB overload made more sense to me

2 pole MCB

RCBO

View attachment 112352

View attachment 112353

My experience is that single gang/ width RCBOs are usually single pole.

O.P I am not a qualified sparky but have some knowledge, experience and some related qualifications and necessary installation testers. I would suggest you leave this alone especially if it is not your boat, there may be other problems with the installation e.g. earthing.

 

[Trident]

Rather than guessing and getting incorrect/dangerous advice, it would be best to post a picture or details from the device, or both.

That said, i suspect it's a single pole RCBO, if you look at the terminals they would be marked something like "L in"," L out" and "N out". If that's the case, the flying lead should be connected to the neutral busbar and the load to the device "N out"

Sorry, yes they are Hager single pole RCBO Type A

Like I said if I had to ask I already know - but the original install was done by a large, qualified and quite well known (locally) company and I wanted to give benefit of the doubt to the way they had wired them. I'll change the N load to the RCBO Out and the pre-wired flying N to the busbar as it should be. Then get someone in to check everything Thank you

 

[PaulRainbow]

As Paul says we don't really know if the unit is a MCB 2 pole or a RCBO which are mainly 2 pole any way.

Which ever way it is to have some loose wiring not connected to any thing does question the knowledge of the original supplier of the consumer unit.

I cannot see a consumer unit being fitted with 10 RCBO which is why a 2 pole MCB overload made more sense to me

Pretty much as Pete says in post #11 it's becoming more and more common to fit RCBOs to each circuit, rather than MCBs, but the RCBOs are single pole, single module. The main supply module has to be double pole though. Not so common on boats, yet.

As you say, wiring not connected is a big no-no.

 

[superheat6k]

Did I read the opening post correctly - all the neutrals go to the busbar and all the earths go to the busbar.

Is this the same Busbar ?

 

[Trident]

Did I read the opening post correctly - all the neutrals go to the busbar and all the earths go to the busbar.

Is this the same Busbar ?

No, consumer units all have separate bus bars for earth and neutral

 

[rogerthebodger]

This looks like one of the RCBO with both Line and neutral connections but only single pole switching

The supply neutral could come from a neutral bus bar but the supply neutral would go to each appliance like this

 

[PaulRainbow]

This looks like one of the RCBO with both Line and neutral connections but only single pole switching

No mention of flying Earth leads in the OP, so not likely to be the same as this, but similar.

The supply neutral could come from a neutral bus bar but the supply neutral would go to each appliance like this

The incoming supply goes to the busbar, the busbar feeds the RCBOs and the loads connect to N out, as i said in post #5 (and David said in post#3)

These are becoming more and more commonplace in domestic installations and as prices continually drop, will likely replace MCBs completely (or thereabouts) before much longer. The ones that you show, with the Earth wire, are more expensive and obviously require more time to fit, there are now more and more versions available without the Earth connection.

 

[VicS]

This looks like one of the RCBO with both Line and neutral connections but only single pole switching

The supply neutral could come from a neutral bus bar but the supply neutral would go to each appliance like this

What is the purpose of the earth connection ?