Electrical set up help required ?

[Nigel B]

Hi all I am in the process of fitting out a 60ft Narrowboat as a live aboard.

As in all these cases asking a question gets many answers that don’t always agree so making the correct and safe choice 

can be difficult so comments on my proposed lay out switch / cable and fuse sizes and placements would be appreciated.

I know there looks to be a lot of rcd in this but they are all as recommended in the insulation manuals. 
I have looked at many articles  here and elsewhere but just want reassurance that iv got things safe and correctly rated.

 

[ditchcrawler]

I would move what you call the shunt/fuse to between the the 300A switch and the battery terminal in the positive line, the actual shunt will probably need to go in the negative and not effected by the fuse.

I would also put a fuse at the junction between the Inverter Master shunt/ Fuse and the 150 amp switch as you may have problems wiring that bit in 70 mm cable

Edited March 16, 2020 by ditchcrawler

[Tracy D'arth]

Seems workable. I agree with ditchcrawler's comments completely. Shunt in negative usually.

You will find the rcds on your 230v supplies from the Mastervolt combi are superfluous I think. I would use rcbos instead for these which will give you over current protection too.

Schneider mcbs and are OK on low voltage DC, used in telephone exchanges.

Do series parallel the batteries so that they all have the same length of cable to positives and negatives, it makes a small but worthwhile difference to the battery life and charging.

[Nigel B]

Thanks for your quick response I will look at your points.

just to clarify the master shunt is the mastervolt master shunt 500 battery monitor system again many thanks.

[ditchcrawler]

You need a fuse adjacent to the battery to protect the cable from the battery

[nicknorman]

People don’t know what a Mastershunt is. I have a Mastershunt and Mastervolt Combi, it is wired thus: from the battery direct to the Mastershunt (+ and - ), keeping these wires short so that the unprotected length is as short as reasonably practicable (my Mastershunt is mounted on the side of the battery box). I wouldn’t put a switch between the battery and the Mastershunt because it is not needed and if you turn it off, you will upset the mastershunt. The MS is designed to be connected to the batteries permanently.

 

Then from the MS to the Combi via a mega fuse (300A I think, ours is 12v 2500w Combi). Since the Combi is also a charger there is no need for any switches between it and the battery, provided it is fused as I describe).

 

Also from the MS to the battery master switch, then on to the dc distribution, fuses etc. The alternator should really be connected to the boat side of the battery master switch, but I moved it to the battery side to avoid the voltage drop across the switch with our big 175A alternator.

 

On the ac side, I don’t see any point or need for RCDs prior to the Combi. We just have the one, after the Combi. What is it that your additional 2 RCDs are protecting against? Too many RCDs spoil the broth, without adding any benefit.

3 hours ago, ditchcrawler said:

You need a fuse adjacent to the battery to protect the cable from the battery

No, the mastershunt provides this.

By the way, will you have a panel (Masterview etc) to allow you to view the data from the Mastershunt? Otherwise, not much point in having it!

Edited March 16, 2020 by nicknorman

[ditchcrawler]

16 minutes ago, nicknorman said:

 .

No, the mastershunt provides this.

By the way, will you have a panel (Masterview etc) to allow you to view the data from the Mastershunt? Otherwise, not much point in having it!

A saw that from later posting but the original drawing shows it at the other end of the cable, you have just told him where it should be

Edited March 16, 2020 by ditchcrawler

[WotEver]

5 hours ago, Nigel B said:

I know there looks to be a lot of rcd in this but they are all as recommended in the insulation manuals.

But installation manuals aren’t system manuals. I don’t see any need for more than one, or possibly two if you also wish to protect the shore power feed through. 

[Steve42]

Regarding the RCD's.

 

The one in the land line I think is or was a requirement for boat safety and should be as  close as possible to the land line to protect the wiring to the inverter.

The travel power output should be protected by an RCD as you have shown. Is the travel power Neutral connected to the chassis and boat ground? if not the RCD won't work.

Not familiar with the Mastervolt,  if it's like my Victron Quattro and the switched output is only ever live on a land line or generator the RCD is superfluous as one of the other 2 will protect the circuits.

The RCD on the Mastervolt inverter output is necessary.

[nicknorman]

10 minutes ago, WotEver said:

But installation manuals aren’t system manuals. I don’t see any need for more than one, or possibly two if you also wish to protect the shore power feed through. 

Yes, for clarity when said we just have the one RCD after the Combi, that is because we only use the one Combi output, we don’t use the one that is only active on shore power. In the OP’s case if he uses both outputs he should have an RCD on each.

[Alan de Enfield]

3 minutes ago, Steve42 said:

The one in the land line I think is or was a requirement for boat safety

Some BSS examiners think it is but IT ISN'T.

 

Having one is an 'advisory' but not a requirement.

[nicknorman]

8 minutes ago, Steve42 said:

Regarding the RCD's.

 

The one in the land line I think is or was a requirement for boat safety and should be as  close as possible to the land line to protect the wiring to the inverter.

The travel power output should be protected by an RCD as you have shown. Is the travel power Neutral connected to the chassis and boat ground? if not the RCD won't work.

Not familiar with the Mastervolt,  if it's like my Victron Quattro and the switched output is only ever live on a land line or generator the RCD is superfluous as one of the other 2 will protect the circuits.

The RCD on the Mastervolt inverter output is necessary.

No, there is no need from either Rec craft directive or BSS to have an RCD before the Combi. What is it you are trying to protect against?

 

if you connect the travel power neutral to ground, you will blow up the travel power. You clearly don’t know what you are talking about so it would be better if you didn’t give dangerous (to the health of the TP) advice. And anyway, there is no need for an RCD between the TP and the Combi. What is it that you are trying to protect against with such an RCD?

3 minutes ago, Alan de Enfield said:

Some BSS examiners think it is but IT ISN'T.

 

Having one is an 'advisory' but not a requirement.

I don’t think it is? It is an advisory to have an RCD between power inlet and appliances, but a Combi isn’t an appliance. You only need (advisorily) to have an RCD between the Combi and the sockets etc. You do not need an RCD before the Combi. What would you be trying to protect against?

Edited March 16, 2020 by nicknorman

[ditchcrawler]

I have never tried it but why wouldn't an RCD work on centre tapped earth, a fault on ether live or neutral conductor to earth will give an imbalance  

[WotEver]

2 hours ago, Steve42 said:

Regarding the RCD's.

 

The one in the land line I think is or was a requirement for boat safety and should be as  close as possible to the land line to protect the wiring to the inverter.

It is not a requirement and is unnecessary. It is part of the fixed wiring, as is the wiring from the travelpower to the Mass Combi. In a house you don’t have an RCD between the incoming tails and the meter, or between the meter and the Consumer Unit; because they would be unnecessary. 
 

The outputs of the Combi must go to consumer units and it is strongly advised that an RCD should be incorporated within the consumer units. It can be an rcbo for simplicity. 

1 hour ago, ditchcrawler said:

I have never tried it but why wouldn't an RCD work on centre tapped earth, a fault on ether live or neutral conductor to earth will give an imbalance  

It would

3 hours ago, Steve42 said:

The travel power output should be protected by an RCD as you have shown.

 No it shouldn’t. It’s entirely unnecessary. 

[WotEver]

2 hours ago, nicknorman said:

I don’t think it is? It is an advisory to have an RCD between power inlet and appliances, but a Combi isn’t an appliance.

Indeed. But I think Alan was speaking more generally about the requirement for any RCD. It’s only advisory but he had an inspector refuse a certificate until he fitted one. He complained to the BSS office but as per usual never received a response. 

[WotEver]

3 hours ago, nicknorman said:

The alternator should really be connected to the boat side of the battery master switch, but I moved it to the battery side to avoid the voltage drop across the switch with our big 175A alternator.

I agree with what Nick describes here although it is a BSS fail if the examiner were to notice (very unlikely). If it connects directly to the battery then the BSS states that it should be fused. So, according to the BSS either connect to the boat side of the master switch or connect via a fuse direct to the batteries. Common sense says connect direct to the batteries without a fuse - just like any car, van, lorry...

[nicknorman]

2 hours ago, ditchcrawler said:

I have never tried it but why wouldn't an RCD work on centre tapped earth, a fault on ether live or neutral conductor to earth will give an imbalance  

It would work. The only “issue” is that since the RCD is measuring earth current (current difference between the conductors), it would require half the leakage resistance (ie a worse fault) to trip, compared to a normal supply (because each conductor is only at 1/2 the voltage). But since the danger to human life is all about current, does this matter? A standard 30mA RCD gives the same protection to human life on a normal supply as on a centre tapped supply, but it is true that a more sensitive (eg 15mA) RCD could be deployed, giving protection against half the current, for  the same degree of nuisance tripping.

 

Since the figure of 30mA is not a magic one, merely a value at which most people won’t be killed, there could be an argument that it is foolish not to take advantage of a centre tapped supply by having a more sensitive RCD.

[ditchcrawler]

10 hours ago, nicknorman said:

It would work. The only “issue” is that since the RCD is measuring earth current (current difference between the conductors), it would require half the leakage resistance (ie a worse fault) to trip, compared to a normal supply (because each conductor is only at 1/2 the voltage). But since the danger to human life is all about current, does this matter? A standard 30mA RCD gives the same protection to human life on a normal supply as on a centre tapped supply, but it is true that a more sensitive (eg 15mA) RCD could be deployed, giving protection against half the current, for  the same degree of nuisance tripping.

 

Since the figure of 30mA is not a magic one, merely a value at which most people won’t be killed, there could be an argument that it is foolish not to take advantage of a centre tapped supply by having a more sensitive RCD.

I agree completely but people often spout "it wont work with a center tap" Its just I have never tried it for myself.

[nicknorman]

14 hours ago, ditchcrawler said:

I agree completely but people often spout "it wont work with a center tap" Its just I have never tried it for myself.

People are wrong!

[WotEver]

8 hours ago, nicknorman said:

People are wrong!

Frequently...

[Nigel B]

I thank all of you for your comments they are things that I will take into account as I put the system together.

I guess there are many ways to skin the cat as they say. But again thanks to this forum there are people out there happy to help and share the knowledge they have gained.

 

[WotEver]

On 17/03/2020 at 09:45, ditchcrawler said:

I agree completely but people often spout "it wont work with a center tap" Its just I have never tried it for myself.

Note that if you ever DO try it yourself that a standard socket tester won’t do it. They have a 6k8 resistor wired from live to earth, assuming a ‘standard’ L & N supply. For Centre-tapped that needs to be a 3k4 resistor. 2W is big enough as long as the RCD trips. 

[ditchcrawler]

37 minutes ago, WotEver said:

Note that if you ever DO try it yourself that a standard socket tester won’t do it. They have a 6k8 resistor wired from live to earth, assuming a ‘standard’ L & N supply. For Centre-tapped that needs to be a 3k4 resistor. 2W is big enough as long as the RCD trips. 

I cant think where I would want to. One day I may see if the RCD trips with no shore line earth connection.  My guess is that it will with a 60 foot of steel in a dirty wet dyke. We use to install ELCBs with just 6 foot of 1" pipe in the ground. I still have one outside my front door.

Trouble is to do that I would need to be on a shore supply

Edited March 18, 2020 by ditchcrawler

[MtB]

On 16/03/2020 at 19:37, nicknorman said:

You do not need an RCD before the Combi. What would you be trying to protect against?

 

A false BSS fail followed by a long and tedious argument about it with the BSS office, perhaps?

 

 

[Keeping Up]

1 minute ago, Mike the Boilerman said:

 

A false BSS fail followed by a long and tedious argument about it with the BSS office, perhaps?

 

 

The BSS office are not completely inflexible. I had a BSS fail on my electrical setup, and as a fully qualified Electrical Engineer I knew that the change that they had made to the rules was based on flawed logic. This was in a fairly similar area, actually the installation and ratings of protection devices before/after the consumer unit. When I contacted them, they gave me a temporary extension to my BSS while they investigated, and after a few weeks they agreed with me and changed their rules again so I passed with no need for a re-inspection.