appropriate or not?

[SparkyTris]

What's wrong with this - if anything? (it is a domestic consumer unit, wired up controlling 24VDC circuits. the breakers are in the Batt positive (+24VDC) line, with the Batt negative (0VDC) line applied to the Neutral busbar.
The red DP breaker breaks both incoming poles, the rest of the MCBs are of course single pole only.

This is on a small fishing vessel on the UK small ships register.

Very many small boats in this general class are wired-up like this, ie using a domestic fusebox as a DC distribution centre.

my general thoughts are, simply from practical experience, that:

these CU's provide an inexpensive and reasonably reliable way of disconnecting the circuits, for technical convenience.

The rating on the MCB should not be relied upon when used in ELV DC operation, because we are no longer on the curve from which the ratings derive, therefore any circuit should be protected with some other overcurrent disconnector appropriate to the nature of the cct.

Notwithstanding the above, these mains-rated MCB's usually *do* seem to operate correctly in fault (overcurrent - normally dead short) conditions in use on ELV DC circuits.

Therefore - in practice, they are OK.

The attached photo was from an installation by a professional and reputable marine electrician in UK.


it has long been a quest of mine to find a rule book regarding ELV and LV wiring for this type of installation. something like the on-site guide ideally. I don't even know whether there is a BS that applies to (coastal) fishing vessels.
IET no use whatsoever. I honestly don't know why I pay my subscription. Vanity I think.

 

[JohnD]

AC devices are generally not suitable for DC. The breakers are not designed to break a DC circuit (the arc is much stronger on DC) and there are curious effects of metals migrating across contacts (this happens on AC as well but it reverses with every cycle)

 

[ericmark]

In the main the circuit breakers used on wagons are smaller push button type with no magnetic release, can't see the point in using domestic cu, I would question if the DC could magntise parts inside the mcb and cause them to trip when they such hold.

I would look at Durite (Gorden Equipment) to see what is on sale for 24 volt DC, also Sterling do a lot of boat stuff.

Most boats I have worked on are two pole, same as fuel tankers. The main problem with boats is heat and fumes. Engine compartments tend to run hotter than wagon, and fumes can be retained, hence why caravan fridges not used in boats.

The is the RCD to consider, and I have not done enough to know all the rules. May be a narrow boat forum could help you?

 

[JohnW2]

The is the RCD to consider, and I have not done enough to know all the rules. ...

Do DC RCD's exist? In any event, is there any point in RCDs with ELV, whether it is AC or DC?

Kind Regards, John

 

[SUNRAY]

What's wrong with this - if anything? (it is a domestic consumer unit, wired up controlling 24VDC circuits. the breakers are in the Batt positive (+24VDC) line, with the Batt negative (0VDC) line applied to the Neutral busbar.
The red DP breaker breaks both incoming poles, the rest of the MCBs are of course single pole only.

This is on a small fishing vessel on the UK small ships register.

Very many small boats in this general class are wired-up like this, ie using a domestic fusebox as a DC distribution centre.

my general thoughts are, simply from practical experience, that:

these CU's provide an inexpensive and reasonably reliable way of disconnecting the circuits, for technical convenience.

The rating on the MCB should not be relied upon when used in ELV DC operation, because we are no longer on the curve from which the ratings derive, therefore any circuit should be protected with some other overcurrent disconnector appropriate to the nature of the cct.

Notwithstanding the above, these mains-rated MCB's usually *do* seem to operate correctly in fault (overcurrent - normally dead short) conditions in use on ELV DC circuits.

Therefore - in practice, they are OK.

The attached photo was from an installation by a professional and reputable marine electrician in UK.


it has long been a quest of mine to find a rule book regarding ELV and LV wiring for this type of installation. something like the on-site guide ideally. I don't even know whether there is a BS that applies to (coastal) fishing vessels.
IET no use whatsoever. I honestly don't know why I pay my subscription. Vanity I think.

Simple solution here.

Buy the right MCB's!!

MCB's are available in DC versions and the voltage is relatively irrelevant.

 

[SFK]

Here are a randomly selected selection of DC rated MCBs (for use in Solar applications)
https://www.shop.solar-wind.co.uk/acatalog/MCB_residual_current_circuit_breakers.html
SFK

 

[SUNRAY]

Here are a randomly selected selection of DC rated MCBs (for use in Solar applications)
https://www.shop.solar-wind.co.uk/acatalog/MCB_residual_current_circuit_breakers.html
SFK

Get from your regular wholesaler, just like i do.

 

[333rocky333]

Theres a few standards refered to in the regs 110.2 (iv) like
https://shop.bsigroup.com/ProductDetail/?pid=000000000030352006

https://shop.bsigroup.com/ProductDetail/?pid=000000000030330463

 

[ericmark]

Do DC RCD's exist? In any event, is there any point in RCDs with ELV, whether it is AC or DC?

Kind Regards, John

RCD = Recreational Craft Directive in my statement sorry should have made it clear. Yes you can get DC residual current devices, but with extra low voltage normally only monitored not auto disconnect.

These are the normal circuit breakers for 24 volt DC, since there are versions with same blades as the blade type fuses one would normally use a blade fuse box and replace fuses with MCB's just like we have done with Wilex fuse boxes with 230 volt for years.

A look at Durite one of the major British firms doing wagon electrical parts and you will see there are many options. this is link for 12/24 volt MCB's also Sterling Power these specialise in boats. I am sure there are many more.

 

[SUNRAY]

RCD = Recreational Craft Directive in my statement sorry should have made it clear. Yes you can get DC residual current devices, but with extra low voltage normally only monitored not auto disconnect.

These are the normal circuit breakers for 24 volt DC, since there are versions with same blades as the blade type fuses one would normally use a blade fuse box and replace fuses with MCB's just like we have done with Wilex fuse boxes with 230 volt for years.

A look at Durite one of the major British firms doing wagon electrical parts and you will see there are many options. this is link for 12/24 volt MCB's also Sterling Power these specialise in boats. I am sure there are many more.

My experience of the ATMstyle plug in trips is they become too sensitive if used near their rated value on a regular basis.
I use the single hole panel mounted trips above to good effect and generally find the tripping current is quite tight and usually go up a size.
In the OP's situation I'd go back to the installers and request the correct MCB's be fitted, if that is not likely to happen then just replace with DC versions. My gut feeling is they may trip too soon as they are.