240 v Mains cable

[Mallard]

I have nearly a full roll of 1 sq. mm twin and earth 240v mains cable. I believe this is rated at 5 amp. So will carry a load in excess of 1Kw.

 

If I use this cable as my low voltage bus at 12v can I assume that it could carry in excess of 80 amps. ??. And do the knowledgeable amoung you think it is suitable

for low voltage distribution?

 

Also, I have seen comments for cable such as "Suitable for AC only". Why?

 

Would much appreciate any guidance.

 

BobM

[Chris116]

When I started doing the electrics on my model railways many years ago, I was taught that you should never use mains cable on the low voltage side as it is too easy to think the mains cable you are just about to touch is low voltage when it in fact is carrying mains voltage which could be rather terminal!

 

Find some good cable that is not used for mains for anything low voltage, just for safety!

 

Chris

[Miss Prism]

I have nearly a full roll of 1 sq. mm twin and earth 240v mains cable. I believe this is rated at 5 amp. So will carry a load in excess of 1Kw.

I think the max rating of that cable is in the 11.5A region. If you use it for 12V d.c., the rating could in theory be (240/12) x 11.5, but I wouldn't count on it, not that you would need such currents anyway. The cable is eminently suitable for low voltage distribution. Chris116's concern is valid only if you have mains and low voltage circuits coexisting within baseboards, and I would think this would be highly unlikely, as well as very undesirable. (If you need a visual difference, strip off the outer sheath.)

[Colin_McLeod]

I have used 13 Amp mains cabled for low voltage bus but having had the same concern as Chris, I used bright yellow cable purchased from B&Q. All my mains cables are white so no confusion. B&Q also sell blue cable. Avoid orange as some mains powered eqiupment comes supplied with orange cable.

 

Another source of heavy duty low voltage wire is the 8A and 10A cable sold in small reels in motor accessory shops. I use this for the cables linking my point motors and CDUs to the accessory decoders.

[Gordon H]

I have nearly a full roll of 1 sq. mm twin and earth 240v mains cable. I believe this is rated at 5 amp. So will carry a load in excess of 1Kw.

 

If I use this cable as my low voltage bus at 12v can I assume that it could carry in excess of 80 amps. ??.

 

NO!!!! The current rating is what it is regardless of voltage.

 

Your assumption is that cable has a constant POWER rating, but this is not the case.

 

The current rating is entirely dependent on the thickness (cross-sectional area) of the copper present, plus an allowance for the effect of the insulation which not only insulates the wire electrically, but also acts as a thermal jacket. Essentially, the ratings you see quoted are for particular wire sizes and the allowable temperature rise for that type of cable when that current passes through it.

Voltage rating is a separate matter entirely, and relates to how much electrical potential can be applied between adjacent conductors before the insulation breaks down and arcing occurs between them. In this respect, the ratings you see are likely to have a reasonably large safety margin, e.g. it is perfectly OK to use a 240V rated wire at 12V because the insulation is more than able to withstand it.

The combination of voltage and current ratings determine what power can be driven into a load at the far end, but each aspect must be considered separately.

[Mallard]

Thanks Gordon H. I felt sure I had got my lines crossed somewhere. Hence the orginal question. Makes perfect sense now.

 

However even at 5 amp rating ( And it would seem 1 sq.mm has a higher rating) it should do the job I want. Does AC or DC make any difference. I do have a reason for asking, and it could be relevant to my wiring method.

 

BobM

[meple]

I have nearly a full roll of 1 sq. mm twin and earth 240v mains cable. I believe this is rated at 5 amp. So will carry a load in excess of 1Kw.

 

If I use this cable as my low voltage bus at 12v can I assume that it could carry in excess of 80 amps. ??. And do the knowledgeable amoung you think it is suitable

for low voltage distribution?

 

Also, I have seen comments for cable such as "Suitable for AC only". Why?

 

Would much appreciate any guidance.

 

BobM

 

 

I would suggest that you take the individual conducters out of the grey sheath so that you don't confuse it with mains cable. The bare copper earth can be used for droppers.

[RFS]

Mains "twin-and-earth" cable is frequently used for the DCC bus. You strip off the outside grey cable and discard the unsheathed copper cable. You can now string the two separate cables underneath the baseboard for your bus, with the wires perhaps 2-3 inches apart. Droppers are then soldered to gaps you make in the insulation.

 

This is what I have done for mine. However, unless your layout is quite small, then 1mm square is a bit on the thin side: I use 1.5mm square for my layout which is 30'x8'. I have a separate bus for the Lenz LS150s points decoders for which I have indeed used 1mm twin-and-earth, but then it's only expected to carry control signals not loco or point motor power.

 

I think you'll find the surplus bare copper earth wire far too thick and impractical for droppers - 7 x 0.2mm or 0.6mm solid (which I use) is fine so long as the wires are short - ie no more than a foot or so. Anything bigger than this is not easy to solder invisibly to the rail.

[RedgateModels]

 

 

I think you'll find the surplus bare copper earth wire far too thick and impractical for droppers - 7 x 0.2mm or 0.6mm solid (which I use) is fine so long as the wires are short - ie no more than a foot or so. Anything bigger than this is not easy to solder invisibly to the rail.

but it is very useful for adding copper piping runs to your BR standard locos or adding that nice pipwork detail in the driving cab (assuming you model kettles that is )

[Penlan]

I have nearly a full roll of 1 sq. mm twin and earth 240v mains cable. I believe this is rated at 5 amp. ......If I use this cable as my low voltage bus at 12v ....

Can we just check what sort of cable you mean, is this the grey, flat, twin and earth single wire 1mm cable used in conduit or trunking behind the studding etc., which if so can be used for up to 2.4Kw* (* See end of posting), or the round 3 wire, multi-strand used to connect lamps, transformers, etc., etc.,

 

Only the former would be suitable (in my opinion) for a BUS(bar) - part of your OP question, one (or two for DCC) wire ran along under the baseboard with dropper wires from the track above connected to it, the BUS being soldered to brass screws proud of the baseboard surface. Obviously the first choice is the unsheathed earth wire, then if for two BUSes, strip the sheathing off another wire.

 

I have a BUSbar, or common return, on my DC/Cab Control layout, all the wires to that side of the track are connected to the BUSbar. Of course with air around the wire, cooling is aided should you up the amps, but hopefully a lot of cut-outs will have clicked in by then - Using your 5 amps figure - if this was regular consumption on a DC layout, it would be a lot - The OP is posted in the Non-DCC section.

 

* 2.4Kw (that is 10amps) this figure is derived by using the calculator here using a length of 20 metres.

[Edwin_m]

Can we just check what sort of cable you mean, is this the grey, flat, twin and earth single wire 1mm cable used in conduit or trunking behind the studding etc., which if so can be used for up to 2.4Kw* (* See end of posting), or the round 3 wire, multi-strand used to connect lamps, transformers, etc., etc.,

 

Only the former would be suitable (in my opinion) for a BUS(bar) - part of your OP question, one (or two for DCC) wire ran along under the baseboard with dropper wires from the track above connected to it, the BUS being soldered to brass screws proud of the baseboard surface. Obviously the first choice is the unsheathed earth wire, then if for two BUSes, strip the sheathing off another wire.

...

 

* 2.4Kw (that is 10amps) this figure is derived by using the calculator here using a length of 20 metres.

 

This is strictly true but could be misleading in the context. The 2.4kW is the rating of the appliances that could be fed by this cable at MAINS voltage. Power equals voltage times current so this would be 10 amps at 240 volts. However as Gordon pointed out above, the limit is to do with current not power, so if the cable is rated at 10 amps at 240V it is also rated at 10 amps at 12V and you could only drive 240 watts worth of 12V equipment with it. Which is still quite a lot in a model railway context.

 

The flex used between plugs and appliances might also sometimes be suitable for use, subject to the same warnings about possible confusion with mains wiring. Its current rating is at least that of the fuse that should have been in the plug it was connected to, usually 5A for lighting and 13A for anything involving a heater. The advantage of flex is that it is multistrand, whereas wiring is single strand and if moved around too much the strand will crack and either cease to conduct entirely or (worse) may start overheating. The flex may have a green/yellow earth, if so I would not use this anywhere on the layout because of the small risk that someone will think it is a mains earth.

[Penlan]

..... so if the cable is rated at 10 amps at 240V it is also rated at 10 amps at 12V and you could only drive 240 watts worth of 12V equipment with it. Which is still quite a lot in a model railway context.

I'am also involved with 6v Austin 7's, so certainly understand it's still only 10 amps at 12 or even 6 volts.

 

I would have thought the individual strand from a multi stranded wire would have been sufficient for a dropper wire to a busbar. Of course this depends how many droppers per length of unbroken rail there are, should be 2 minimum - I seem to recall Jim s-w dealing with this topic some time ago.

 

I can't see where one would use fully sheathed mains cable under a layout for 12 volts, or have I missed something in my 60 years of modelling.

[Edwin_m]

I wasn't questioning your own understanding Penlan, but I felt that someone with less experience could conclude from your post that there was no problem with using this cable for very high currents at low voltages.

 

I also agree if you are to use either cable or flex it would be best to remove the outer sheath.

 

However I don't think that an individual strand from a multi-strand wire would be suitable for anything except perhaps a LED or two. I've never heard of any droppers thinner than 7/0.2 and the rating of a single strand would surely be much less than the current drawn by a typical motor.

[Mallard]

I suppose it might help if I come clean on what I am trying to do. But am I hijacking my own thread?

I have available the Aristocraft HO controller system. This is a radio control. Not DCC. The system requires a 12 volt dc supply.

However I wonder if an ac supply of about 16v rms converted in the loco thru a bridge rectifier before feeding the aristocraft radio controlled chip might be a better,or simpler way of supplying the necessary power. The controller is hand held and wireless. So I reckon I need a 4 or 5 amp steady supply of approx. 12v. If I use ac I think loops etc. will be much easier to wire. Now you can all tell me I'm crackers.

BobM

[298]

I can't see where one would use fully sheathed mains cable under a layout for 12 volts, or have I missed something in my 60 years of modelling.

 

I've used orange twin for 12v halogen lighting (sold as flex for double insulated garden tools), that's where you can get a real current draw. It's use was passed off by one of the better electricians I work with, and only caused a problem at one show where it was thought to carry mains voltage.

 

Saying something is fine just as long as the builder knows what it's for and the casual observer can soon work out that something coming out of a 12v transformer and going through 10A connectors to low voltage halogen lighting should cover all eventualities, although I bet there are still some daft wiring examples out there- I remember reading a good few years ago of a control panel with a 3 pin socket on the side used for the mains input, with presumably an extension cord with 13A plugs on each end....

[melmerby]

so if the cable is rated at 10 amps at 240V it is also rated at 10 amps at 12V and you could only drive 240 watts worth of 12V equipment with it. Which is still quite a lot in a model railway context.

 

 

Sorry but 10A x 12V = 120W not 240W but bear in mind DCC is usually about 15v equivalent AC at track, so 150W with 10A rating.

 

Some top end DCC systems have 15v @ 8Amps output which is 120W so not over the top after all!

 

There seems to be a lot of confusion about amps volts and watts on the posts on RM web as this sort of thing has cropped up before.

PS how would any body confuse a T&E cable under the layout for mains carrying cable, mains carrying T&E shouldn't be there.

 

Keith

[Dagworth]

If I use ac I think loops etc. will be much easier to wire. Now you can all tell me I'm crackers.

BobM

 

It makes no difference at all for wiring of loops whether AC or DC or DCC is used. You still have to ensure that the left hand wheels are fed from a different pole to the right hand wheels.

 

Andi

[AMJ]

The only time that AC or DC works when feeding loops without any switching is if both rails are the same polarity and you have a common return a la Marklin via studs (or 3rd rail).

[Pinkmouse]

Saying something is fine just as long as the builder knows what it's for and the casual observer can soon work out that something coming out of a 12v transformer and going through 10A connectors to low voltage halogen lighting should cover all eventualities, although I bet there are still some daft wiring examples out there....

 

 

IIRC, using standard mains, (low voltage) coloured cable for ultra low voltage runs is theoretically against 16th Ed. rules and a PAT test failure. I've certainly been caught out by the opposite, when I used Socapex multicore lighting cables on an exhibition stand at the NEC. It does not use regulation colours, and because of that could be thought to cause confusion, so according to the NEC electricians, now has to be carried in metal trunking under floors wheras T+E is fine to run loose.

[meple]

IIRC, using standard mains, (low voltage) coloured cable for ultra low voltage runs is theoretically against 16th Ed. rules and a PAT test failure. I've certainly been caught out by the opposite, when I used Socapex multicore lighting cables on an exhibition stand at the NEC. It does not use regulation colours, and because of that could be thought to cause confusion, so according to the NEC electricians, now has to be carried in metal trunking under floors wheras T+E is fine to run loose.

 

 

Its been the 17th edition since 2008.

[Penlan]

......., when I used Socapex multicore lighting cables on an exhibition stand at the NEC. It does not use regulation colours, and because of that could be thought to cause confusion, so according to the NEC electricians, now has to be carried in metal trunking under floors wheras T+E is fine to run loose.

Though I obviously don't know all the circumstances, but presumably you were also using Socapex multipin connectores - I wonder how the NEC Electricians get on with the stage lighting for the likes of Tom Jones, Barbara Streisand, West Life, etc., etc., As I recall a lot of that's done using Socapex cables and connectors, plus of course the 3 round pin IP44 rated (EN 60309-2, IEC 309-2, CEE7) plugs and sockets for individual items. I use these for my layout lighting too.

[Edwin_m]

Sorry but 10A x 12V = 120W not 240W but bear in mind DCC is usually about 15v equivalent AC at track, so 150W with 10A rating.

 

Some top end DCC systems have 15v @ 8Amps output which is 120W so not over the top after all!

 

There seems to be a lot of confusion about amps volts and watts on the posts on RM web as this sort of thing has cropped up before.

PS how would any body confuse a T&E cable under the layout for mains carrying cable, mains carrying T&E shouldn't be there.

 

Keith

 

Oops. You are correct re the 120W though as this is in the non-DCC electrics forum I think we are discussing 12Vdc here.

[Penlan]

......PS how would any body confuse a T&E cable under the layout for mains carrying cable, mains carrying T&E shouldn't be there.

Just to clarify my use of the T&E (Twin & Earth flat grey) cable for a BUS, I was suggesting using the individual solid wire stripped out of the sheathing, it could just as easily be some brass 1mm square bar/round wire from say Eileen's Emporium, but that would be a lot more expensive and is only available in short lengths.....

[melmerby]

Just to clarify my use of the T&E (Twin & Earth flat grey) cable for a BUS, I was suggesting using the individual solid wire stripped out of the sheathing, it could just as easily be some brass 1mm square bar/round wire from say Eileen's Emporium, but that would be a lot more expensive and is only available in short lengths.....

 

There were some earlier posts in this thread about confusing cable carrying track power with mains power if using mains type cables.

My comment was why would anybody have mains bearing cable, especially T&E in such a situation that you could touch the bare wires!

Twin & Earth is for fixed wiring only i.e. sunk in walls or cleated in position, not to be used as flex.

 

I am using ex house wiring T&E (still in sheath) for my layout bus as it will carry the current adequately and will not be confused with the flexes carrying power to the various transformers etc.

 

Keith

[melmerby]

Oops. You are correct re the 120W though as this is in the non-DCC electrics forum I think we are discussing 12Vdc here.

 

Using mains cable for bus wiring could apply to either system and DCC had been mentioned in a couple of the replies so I was just trying to clarify the power requirements.

 

Keith