cable capacity for switched power supplies

[wasdavetheroad]

I find elektrical trickery confusing so can I do this without burning the layout room down.

 

Present situation - I have 3 additional 240V LED lights wired in parallel to a switched 13A socket using 3A cable, needing about 0.5A?, works great

 

I want to change this to add 2 x 12V switched power supplies for point motor control, one in the scenic section and one in the fiddle yard.

 

The point motors are Kato with Kato passing contact switches. They run on 12V DC. a maximum of 2 motors will be switched simultaneously.

 

The 2 power supplies I have are;

A BT router one, input 240V AC 300mA, output 12V DC 1.5A

An APD? one, input 240V AC 850mA, output 12V DC 1.5A

 

I have tested the BT one and it fires 2 point motors no problem.

 

I plan the connections to be from the 13A socket to a 4 way 13Amp individually switched power strip and from 3 plugs on there to the lights and the power supplies.

 

Advice on problems please and what cable will I need to connect the power supplies which are up to 5 metres from the sockets.

[cliff park]

So the BT one and the APD one together add up to 1.15A approx. But this is only when 'loaded 'up. Ie most of the time they take negligible current. It wouldn't hurt to uprate your cable if you have multiple sockets, there is always the chance somebody will plug a fan heater or something similar in, or at least make sure the fuse in the plug is 3Amp.

[Nigelcliffe]

 

Unlikely to be a problem, unless your layout is massive, or hides an electric heater in the middle of it.....

 

Before lockdowns, I was working on the wiring for Burntisland 1883.  Its a huge Scalefour layout, over 12m x 6m, with a 5A Lenz DCC system, dozens of turnout motors, at least 16 PSUs for different things around the layout, a microprocessor controlled lighting rig for the entire layout (many 10s of meters of LED strips).      That lot came to under 4Amps at the mains socket (measured with a cheap plug-in power consumption "brick" with a readout on it).   

 

A typical 240v LED lamp will be 5Watts or so, perhaps 10Watts for a really bright one.   24 lamps at 10W each is 240Watts, which at 240volts mains is 1Amp.

 

 

Mains stuff - I'd always use decent cable, rated for the full 13A, with sockets of decent quality.   Then, if it gets "borrowed" for a kettle or similar, it won't be a problem.  

 

 

- Nigel 

[wasdavetheroad]

The layout is in a converted garage and has a supply laid on, the attached images may help. the armoured cable is about 14mm diameter.

 

Power needs in the garage are 1 or occasionally 2 x 1Kw fan heaters,1 used for frost protection and one to 'top up' if needed 2 x 4ft florescent tubes and 1 bulb with switches on the wall.  Four switched wall sockets and 3 extra lights from one of the sockets. I want to add the 2 power supplies . There is no track power as the layout will be radio control/battery powered locos.

 

No idea what the numbers mean on the circuit breakers. I think the 7Kw electric shower pinched the cooker circuit!.

 

 

[AndyID]

As Cliff and Nigel have said the two switched-mode PSUs will not draw very much current at all and it will be well within the capability of any good quality extension lead. However, it might be safer to avoid using any mains extension leads by extending the low voltage outputs of the PSU's instead.

[wasdavetheroad]

That's an interesting suggestion. I have tested the output of the PSU's and they are stable at just below and just above 12V. I will have a go at extending the 12V output with good capacity wire, probably cable and check the voltage drop and whether it will still fire a pair of point motors.

 

Thanks again

[Michael Hodgson]

Building restrictions were tightened some years ago and only a qualified person is now allowed to do most jobs on the mains, or at least it has to be inspected by one and the cost is much the same - especially work on outbuildings, kitchens and showers.  I'd be very worried if you were a qualified sparky and need to ask about this, so I assume you should be leaving all that well alone.  In any case it doesn't look like a problem.   As to what the markings on your mains fitments mean,

• B6 is a 6 Amp circuit breaker - typically used for lighting circuits, often one upstairs another downstairs (it's a good idea to label what each one does) 
• B32 is a 32 Amp circuit breaker - typically used for the ring main supplying sockets.  Again often one upstairs another downstairs.  A cooker also often uses a third. 
• A 7kW shower needs to be on its own direct circuit, not a ring main, and 7kW as about 30 Amps, so yes, it may well have nicked the cooker circuit if you're using gas to make your dinner 

Outbuildings like garages should have their own little consumer unit ("fuse box"), with similar circuit breakers, so typically as your third photo

• 6Amp one for the garage light
• 32 A for sockets

The lead supplying the garage should have a circuit breaker in the house, and outbuildings are often limited to the 20A in total, as seen in your second photo.

 

To deal with your point motor supply, I'd endorse what Nigel says.  The load it draws is negligible; the main load in your garage is those two 1kW fan heaters - they use a lot more power than any model railway that will fit in a garage.  Don't forget that transformers don't just reduce the voltage, they increase the output current - 1.5 Amps at 12v is equivalent to only 75 milliamps at 240v

 

[wasdavetheroad]

Thanks everyone, I think I understand it now and I don't have to add the extension leads etc until the new garage side door is fitted