Wiring a 240V MCB box

[BargeeSpud]

Hiya,

 

Several years ago, I fitted a domestic MCB fuse box as part of my 240V circuit. Unfortunately, its never worked whenever I connected my generator to the boat's landline socket but since I haven't had need to use it that often & found it easier to use the equipment via an extension lead direct to the gennie, it hasn't bothered me too much.

 

Now I'm going to live aboard, I will probably have need of it, so my question is this:

 

What is the correct way to wire it up?

 

I think (I haven't checked yet) that I probably wired it as for a domestic set up & I have heard that this is incorrect for a narrowboat installation & I have a galvanic isolator attached.

 

Can anyone advise me as to how the positive, negative & earth cable should be connected so that the thing will not trip out every time I connect the gennie. Unfortunately I have never been able to hook up to shore based power, so can't be sure whether its the gennie or my wiring thats causing the problem.

 

Cheers.

[Arthur Brown]

Your domestic MCB dis board will not have facility for two alternative mains feeds, It's intended to take mains and distribute it.

 

One sensible method is to bring the shoreline onboard to a 16A appliance inlet. then sent this to the dis board. Use a shorter lead to connect the generator to the same place, when off mains.

Several other manual or automatic methods exist for sending only one of the possible supplies to the consumer unit.

Edited September 13, 2012 by Arthur Brown

[BargeeSpud]

Your domestic MCB dis board will not have facility for two alternative mains feeds, It's intended to take mains and distribute it.

 

 

Several other manual or automatic methods exist for sending only one of the possible supplies to the consumer unit.

CONSUMER UNIT! Of course! Good grief now I know I'm getting old when I can't drag up the proper name for what I'm asking about.

 

Q1. What if the gennie is the only source of 240V?

 

Q2. Can you point me in the direction of where I can find these "other methods"?

Edited September 13, 2012 by Spuds

[Arthur Brown]

Assuming that the consumer unit is secure and properly wired, find a place to fit a surface mount appliance inlet (that means it has exposed pins and fastens to the wall) where it is convenient and safe to bring the power onboard with a lead. Whether your power comes from mains hookup or generator plug it into the appliance inlet.

 

There are some switch unite designed to take mains input and generator input and allow you to switch manually, -some more expensive than others. There are auto transfer switches in the UPS industry but they are expensive compared to the boat!

[BargeeSpud]

Assuming that the consumer unit is secure and properly wired, find a place to fit a surface mount appliance inlet (that means it has exposed pins and fastens to the wall) where it is convenient and safe to bring the power onboard with a lead. Whether your power comes from mains hookup or generator plug it into the appliance inlet.

 

 

OK, how do I wire that into the consumer unit or the 240V circuit?

[Gibbo]

http://smartgauge.co.uk/nb_ac_sys.html

[OldGoat]

http://smartgauge.co.uk/nb_ac_sys.html

 

 

Lordy, lordy, that looks quite complicated (especially for folks who are fazed by 'lectrickery)

My solution - and I'm still around to prove that it's not dangerous is to have a multi pole rotary switch (wih break before make contacts) which selects mains, inverter1, inverter2 as the power source.

This feeds directly into a garage/ site supply consumer unit with a RCCD trip and 3 MCBs.

 

Has worked succesfully for the last 12 years with no tripping.

 

I'm wondering whether it's the genny that's causing the circuit to trip??

 

I always start / connect the source power first and THEN switch to select it (I once heard that inverters in particular caused a spike when they start which can blow tv etc.

 

Perhaps the OP could try that method before chucking all his kit away?

[WotEver]

... have a multi pole rotary switch (wih break before make contacts) which selects mains, inverter1, inverter2 as the power source.

That's exactly what the 6th and 7th diagrams show.

 

Tony

[OldGoat]

That's exactly what the 6th and 7th diagrams show.

 

Tony

 

 

You're probably right, but there's such a mix of RCD / MCBs duplicated - for no good reason as far as I can see; certainly would confuse a non electrician - that I lost the will to live.

I didn't stop to work outr the advantage of such duplication.

 

 

 

I always rely on the KISS principle....

[Paul C]

that looks quite complicated

 

 

certainly would confuse a non electrician

 

 

While I'm all for encouraging DIY, if its something significantly above your level of skill then I'd suggest you have someone else (who's skilled and experienced with boat mains electrics) to do it. If it were only a couple of questions to fill in the 'gaps' in your knowledge, then by all means asking stuff on an internet forum could help you so you're confident of it. But trying to learn it from no knowledge, and getting it right first time AND safe, is a big ask.

 

The diagrams aren't complicated, they go from simple ways to wire it, to more complex ones with more 'features' that these days are in demand on boats.

 

Having said all that, it does sound like your generator might be tripping the RCD anyway, so it would continue to trip an RCD if wired correctly; pointing towards a fault or miswiring of the generator. Might be worth getting it checked over properly.

[Arthur Brown]

If the drawings that Gibbo posted don't make sense to you then please get help with the installation. There is a lot of sense in there and no "spare" parts. They vary from all mains to mains and two inverters with only the essential parts used.

[BargeeSpud]

Thanks for all the responses & I've taken them on board. The link by Gibbo is actually useful even though confusing, as there are other links on there that explains some of it, especially earthing. I think that could be my problem, I'm not sure if the earth on the consumer unit is attached to the hull, I know the galvanic isolator is. Will check as soon as.

 

Never mind onboard generators, inverters etc., all I want to do right now is hook up my gennie to the boat's landline socket, plug in & go without the chuffin' trip banging out. Let you know how I get on

[rjasmith]

Thanks for all the responses & I've taken them on board. The link by Gibbo is actually useful even though confusing, as there are other links on there that explains some of it, especially earthing. I think that could be my problem, I'm not sure if the earth on the consumer unit is attached to the hull, I know the galvanic isolator is. Will check as soon as.

 

Never mind onboard generators, inverters etc., all I want to do right now is hook up my gennie to the boat's landline socket, plug in & go without the chuffin' trip banging out. Let you know how I get on

 

Presumably the "trip" in your consumer unit is an RCD (or perhaps an RCBO?). Is it this that trips when you plug the gen. output into the shoreline input?

 

Do you have any sort of diagram for how you connected the CU and its MCBs/RCD up and also what make of generator is it and how is it earthed (also does it have an N-E bond)?

 

It might help folks on here sort out why the tripping is happening if you can show how you've connected everything.

 

Rather difficult to do otherwise!

 

Richard

[BargeeSpud]

Presumably the "trip" in your consumer unit is an RCD (or perhaps an RCBO?). Is it this that trips when you plug the gen. output into the shoreline input?

 

Do you have any sort of diagram for how you connected the CU and its MCBs/RCD up and also what make of generator is it and how is it earthed (also does it have an N-E bond)?

 

It might help folks on here sort out why the tripping is happening if you can show how you've connected everything.

 

Rather difficult to do otherwise!

 

Richard

I appreciate that Richard, so as soon as I get down there again, I'll come back with a circuit diagram/description of whats connected to what.

 

In the meantime, yes its the main RCD that trips when I place a load on the circuit, it doesn't trip with the gennie connected without a load. My gennie is a Honda EU20i & I don't earth it (didn't know you had to) & I don't know what an N-E bond is.

 

Cheers.

[rjasmith]

I appreciate that Richard, so as soon as I get down there again, I'll come back with a circuit diagram/description of whats connected to what.

 

In the meantime, yes its the main RCD that trips when I place a load on the circuit, it doesn't trip with the gennie connected without a load. My gennie is a Honda EU20i & I don't earth it (didn't know you had to) & I don't know what an N-E bond is.

 

Cheers.

 

Well an EU20i has a splendid reputation but I don't own one so can't really help about its earthing arrangements - you could look at its manual perhaps!

 

I think you ought to spend a little time reading up about these things and would really recommend Gibbo's website Technical Info pages. It's all in there somewhere and worth trying to absorb if you can! The pages he's already linked to should make it clear how your connections should have been done.

 

Rather than me trying to explain a Neutral - Earth bond here, Gibbo's pages will already have done it, probably better than any attempt of mine!

 

Richard

[Richard10002]

I have an Eu20i that I plug into the shoreline socket, from where it goes to a consumer unit, then the inverter charger. I use the generator as it came out of the box, and nothing trips.

[rjasmith]

I have an Eu20i that I plug into the shoreline socket, from where it goes to a consumer unit, then the inverter charger. I use the generator as it came out of the box, and nothing trips.

 

Ah but if there is a fault to earth somewhere in your boat while running off the generator have you checked that the RCD will trip?

 

Richard

[Arthur Brown]

Any form of RCD or RCBO will only trip if the supply is correctly earth referenced. If you don't understand this then please get help, because a typical generator (under 6KIVA ) will not be earth referenced unless you do the job and so the protection that you rely on may not work.

[RLWP]

You're probably right, but there's such a mix of RCD / MCBs duplicated - for no good reason as far as I can see; certainly would confuse a non electrician - that I lost the will to live.

I didn't stop to work outr the advantage of such duplication.

 

 

 

I always rely on the KISS principle....

 

Did you read any of that website? For instance, this bit:

 

One word of warning. Do not be tempted to overcomplicate things. Try to keep it as simple as possible. Simplicity in this case is usually elegant. And an elegant design usually works better than anything else.

 

Richard

[smileypete]

In the meantime, yes its the main RCD that trips when I place a load on the circuit, it doesn't trip with the gennie connected without a load. My gennie is a Honda EU20i & I don't earth it (didn't know you had to) & I don't know what an N-E bond is.

If you press the test button briefly when the power is on, does it NOT trip? If so this can indicate a mis-wired RCD which will always trip under load (and blow up the test circuit if you hold the test button down ).

 

If it trips OK on the test button then try a plug-in socket tester to check if the earth is OK, if it's floating/disconnected it may cause all manner of strangeness

 

cheers,

Pete.

[Richard10002]

Ah but if there is a fault to earth somewhere in your boat while running off the generator have you checked that the RCD will trip?

 

Richard

 

How would I generate a deliberate fault to earth, (the hull is the earth in my case). Presumably, touch a live wire to the hull, but there is presumably a safe way of doing this?

 

The plug that goes into the generator has an earth, and this earth connects to the earth in th consumer unit, which connects to the hull earth point... If that means anything.

[gazza]

In my dads words.....

Lectrics Is easy, red to red, black to black, blew to bits.

 

Not being funny, but your posts give the impression that you are not very clued up where electrical installations are concerned

 

Best advice is to consult an electrician, sorry if thats a bit blunt but by page two and you are still unsure of the potential problems with a very simple set up suggests you need expert help.

[Richard10002]

In my dads words.....

Lectrics Is easy, red to red, black to black, blew to bits.

 

Not being funny, but your posts give the impression that you are not very clued up where electrical installations are concerned

 

Best advice is to consult an electrician, sorry if thats a bit blunt but by page two and you are still unsure of the potential problems with a very simple set up suggests you need expert help.

 

Are you talking to me? Or to the OP? Or someone else.

 

If me, I don't disagree, but all I've done is bought a generator and plugged it in. Someone says that may not be safe, and there seems to be a simple test, so I ask how to do it safely. After the test, if I need an electrician, I'll get one.

 

Many Thanks,

 

Richard

[smileypete]

How would I generate a deliberate fault to earth, (the hull is the earth in my case). Presumably, touch a live wire to the hull, but there is presumably a safe way of doing this?

 

The plug that goes into the generator has an earth, and this earth connects to the earth in th consumer unit, which connects to the hull earth point... If that means anything.

Just wire a normal 60W bulb in a holder to live and earth in a 3A fused plug, see if it trips the RCD. Then check for good continuity between the earth terminal on a socket and the hull. A plug in socket tester might also quickly tell if some sockets have a floating/disconnected earth.

 

Once I wired up a fan heater plug whilst on the phone listening to the parents, and the resulting drowsiness caused me to wire it up to the live and earth terminals. I soon realised the error of my ways when I came off the phone, plugged it in and was plunged into darkness and silence!

 

cheers, Pete.

~smpt~

Edited September 15, 2012 by smileypete

[rjasmith]

How would I generate a deliberate fault to earth, (the hull is the earth in my case). Presumably, touch a live wire to the hull, but there is presumably a safe way of doing this?

 

The plug that goes into the generator has an earth, and this earth connects to the earth in th consumer unit, which connects to the hull earth point... If that means anything.

 

I was going to say something similar to smileypete but have been busy on other things today. Another way to do a test might be to beg, borrow or steal a proper RCD tester, perhaps even persuading its competent owner to do the test for/with you!

 

In the meantime how about a link to a rather good tech article on RCDs etc in the IET's "Wiring Matters". Link is here and you will need to temporarily download the .pdf file.

 

The article might be a bit technical for some but I thought it explained the whole subject of RCDs in an easy to follow manner.

 

Richard