Best cable for 240v circuit

[Polishicebreaker]

Hi, I searched a few threads but couldn't find what I was after.

I've done a fair bit if research on cable for DC on boats but no naff all about AC. This will be for a circuit all over boat with genny connections bow and stern and a couple of sockets in the cabin. Any cable recommendations? Not standard household I imagine

[Puddlejumper]

2.5mm 3core flex clipped up every 150mm or run through trunking wont give any problems if fitted properly and back to a fused dis unit as a ring main) best through trunking if you have the space then you can add if needed later

Edited March 30, 2015 by Puddlejumper

[Keeping Up]

Definitely use flex and NOT house wiring cable. Most people use "Arctic" cable.

[Puddlejumper]

Just a quick note do Not put any pvc cable through polystyrene insulation as it will eat the pvc

[nicknorman]

Hi, I searched a few threads but couldn't find what I was after.

I've done a fair bit if research on cable for DC on boats but no naff all about AC. This will be for a circuit all over boat with genny connections bow and stern and a couple of sockets in the cabin. Any cable recommendations? Not standard household I imagine

2.5mm 3 core flex as mentioned. Just remember that if you have genny connections at bow and stern, they need to be switched so that the connector(s) not in use is/are not live.

[OldGoat]

To do the job properly you must have a consumer unit in the circuit and the generator/s feed into that before the sockets. Again each of those two must be separate and selected before the consumer unit.

 

I suspect that's not going to happen...

 

anyway the question was about which cable. Arctic is more substantial than normal 3 core flex - so why not use it. logically it should be in trunking. Which ever way you do the job, you must use bootlace ferrules in the sockets. Domestic sockets were designed for single strand cables and don't work well with multi strand flexible cables.

[Guest]

2.5 mm sq 3 core arctic flex gets my vote. No need for a house style "ring main" on boat installations, can allegedly cause interference off inverters.

Edited to add I agree that bootlace ferrules are good plan on flex.

Edited March 30, 2015 by Guest

[Polishicebreaker]

great thanks but what the heck are bootlace thingymabobs?

[Arthur Brown]

Cable - 2.5mm^2 blue arctic flex pulled in trunking, separated from lower volts (12v and data) carefully.

 

Feeds - the correct connector for feeding electricity into a boat is an "appliance inlet connector" which has exposed pins so unless you pay silly money for switched interlocks then take both appliance inlets back to the consumer unit and separately feed the forward and aft mains and the generator input and the inverter connection into a multipole switch to chose only one input.

 

notes;

Mains as supplied at the bollard is ground referenced so must not have another ground reference connection. the generator is likely NOT ground referenced so needs to be checked but likely needs a ground reference connection on the boat to let any RCDs work properly. The inverter is likely to be without ground reference -check it and it's book. A Travel Power is likely to be 240v centre tapped earth -really it's not compliant with mains.

[GUMPY]

great thanks but what the heck are bootlace thingymabobs?

Goes on the end of the wire to protect the strands from screw damage

[Keith M]

I use 2.5 mm² H07 RNF for socket outlets. Please do not install a ring main but radial circuits instead these are much safer

If you use an arctic type cable ensure that it conforms to BS 7919

 

And always use boot laces or cable ferrules displayed above.

 

Please PM if you require any further information

 

Keith

[jonathanA]

I use 2.5 mm² H07 RNF for socket outlets.

 

Keith

Why where's the need for such a heavy duty / abrasion resistant cable in fixed cabling on a boat ?

 

I think artic is usually used for its 'blue' colour more than it's specification which isn't really relevant in a boat situation IMHO

 

Can't see how the significant extra cost of ho7 is justified tbh

[frangar]

Given that boats are subject to vibration and possibly extremes of temperature I don't think using HO7 is overkill....and hopefully you are only going to fit it once!

 

Cheers

 

Gareth

[Keith M]

I work on many vessels during my working year both inland and blue water

 

Unfortunately most inland installers do not clip the cable as recommended or separate it from the DC cabling.

 

This is one of my pet hates

 

Keith

[Murflynn]

I work on many vessels during my working year both inland and blue water

 

Unfortunately most inland installers do not clip the cable as recommended or separate it from the DC cabling.

 

This is one of my pet hates

 

Keith

ISO EN/BS standards require 240AC multistrand (arctic) cables with ferrules separated from DC wiring, as I recall.

This is required for RCD compliance, so presumably 'most inland installers' are automatically contravening the RCD requirements.

[nicknorman]

ISO EN/BS standards require 240AC multistrand (arctic) cables with ferrules separated from DC wiring, as I recall.

This is required for RCD compliance, so presumably 'most inland installers' are automatically contravening the RCD requirements.

I think there is some grey area about separating the ac and dc. You can put one in amongst the other provided it is seperately trunked, eg big trunking containing lots of DC wiring, small trunk inside the big trunk containing ac wiring. It then falls to what is a trunk, and it seems that the fact that the ac wires are not only individually insulated, but also have an overall insulating sheath (aka trunk) that is the get-out ploy.

[Arthur Brown]

Single strand cable needs trunking with others of the same voltage rating, Sheathed cable can be run with other sheathed cable. If you run sheathed cable and single strand in the same trunk then all of all of the systems should be rated for the highest voltage present.

[Keith M]

ISO EN/BS standards require 240AC multistrand (arctic) cables with ferrules separated from DC wiring, as I recall.

This is required for RCD compliance, so presumably 'most inland installers' are automatically contravening the RCD requirements.

You are right Sir

 

 

Keith

Edited April 6, 2015 by Keith M

[Keith M]

I think there is some grey area about separating the ac and dc. You can put one in amongst the other provided it is seperately trunked, eg big trunking containing lots of DC wiring, small trunk inside the big trunk containing ac wiring. It then falls to what is a trunk, and it seems that the fact that the ac wires are not only individually insulated, but also have an overall insulating sheath (aka trunk) that is the get-out ploy.

AC and DC cables should be separated by 100 mm

 

Please refer to the BMEEA Code of Practice 2.7.8

 

Keith

[nicknorman]

AC and DC cables should be separated by 100 mm

 

Please refer to the BMEEA Code of Practice 2.7.8

 

Keith

I am not familiar with the BMEEA code of practice as it is just that, a code of practice for a club, and to join that club and get their CoP you of course have to pay money. The CoP is not the regulations which I believe are ISO 13297 for RCD compliance. Certainly separation by 100mm is one means of compliance, but there are others including seperate trunking and it does actually say seperate sheathing, so I guess running sheathed ac cable in amongst dc wiring is in fact allowed (provided insulation voltage rating is satisfactory). I don't have access to the BMEEA CoP but I would be very surprised if separation by 100mm was their sole means of compliance.

[Keith M]

Hello Nick,

 

Any person can have a copy of the C of P it is just not for club members as you put it.

 

 

Contact the BMF and they will happily sell you a digital copy C of P which has both the ISO and guidance notes. It is also I believe the cheapest way of buying both ISO's.

 

I was part of the UK team which help with the revision of both ISO which were published mid 2013.

 

From what you have stated you have seen some of if not all of the AC ISO and it clearly talks about different forms of cable separation. Not installing AC and DC cables within the same space.

 

Keith

[nicknorman]

The copy of the ISO I have is not the latest version, but it says:

11.3 An a.c. circuit shall not be contained in the same wiring system as a d.c. circuit, unless one of the following methods of separation is used.

a) For a multicore cable or cord, the cores of the a.c. circuit are separated from the cores of the d.c. circuit by an earthed metal screen of equivalent current-carrying capacity to that of the largest core of the a.c. circuit.

b ) The cables are insulated for their system voltage and installed in a separate compartment of a cable ducting or trunking system.

c) The cables are installed on a tray or ladder where physical separation is provided by a partition.

d) A separate conduit, sheathing or trunking system is used.

e) The a.c and d.c. conductors are fixed directly to a surface and separated by at least 100 mm.

 

So as I read it, para d) allows an ac cable with overall sheathing (eg flex type 3 conductor cable) to be mixed in with dc wiring. Unless the latest version says different?

Edited April 6, 2015 by nicknorman

[Keith M]

Hello,

 

Both old and new versions are similar.

 

Para D: As the sentence starts by talking about using conduit to form the separation between AC and DC cables surely the rest of the sentence is also talking about using conduits, trunking etc. as forms of separation. The sheath in my opinion refers to a type of flexible conduit around either AC or DC cables.

 

Surely you can except that it is poor practise to install both AC and DC in the same cable space.

 

It may be expectable to use an SY Multi Flex cable.

 

Keith

[nicknorman]

Hello,

 

Both old and new versions are similar.

 

Para D: As the sentence starts by talking about using conduit to form the separation between AC and DC cables surely the rest of the sentence is also talking about using conduits, trunking etc. as forms of separation. The sheath in my opinion refers to a type of flexible conduit around either AC or DC cables.

 

Surely you can except that it is poor practise to install both AC and DC in the same cable space.

 

It may be expectable to use an SY Multi Flex cable.

 

Keith

Hi Keith

 

My points were not addressing what might be good or bad practice, rather what is or is not permitted under the regs and how some installers consider use of sheathed cable mixed in with DC wiring to be compliant, based on d). I can't say what the intent of that para is but if it means flexible conduit then I think it should say that, because whilst you could call flexible conduit "sheathing", that word is commonly used to describe the overall insulation around a 3 conductor flex cable.

 

As to my personal opinion (which is not of any value in the great scheme of things!) on the merits or otherwise of mixing flex cable carrying ac, with DC, the issues as I see it are:

Should a short circuit develop between ac and dc, the RCD should operate (provided the mixed wiring is post-RCD)

Flexible conduit is quite hard and sharp and whilst it will protect the wiring within, has the potential to damage adjacent cabling outside it

One can choose 2 methods of avoiding adjacent cable damage, either effectively armouring each wire by encasing it in (eg) flexible conduit or, by ensuring there is no relative movement between wires (eg by tywrapping everything together at frequent intervals, ensuring adequate strain relief at the ends).

 

So provided my last bit above is done, I don't see a significant hazard of mixing dc wiring with overall-sheathed ac wiring compared with the risk from say a kettle flex cord handled with wet hands in the kitchen.

[Murflynn]

Single strand cable needs trunking with others of the same voltage rating, Sheathed cable can be run with other sheathed cable. If you run sheathed cable and single strand in the same trunk then all of all of the systems should be rated for the highest voltage present.

all boat wiring should use multi-strand cable. I think you mean single core.