Which gauge SWA & other outdoor questions

[Colin M]

Work is about to start on hard landscaping in my garden and there is a gazebo and shed planned for one corner.

My plan is to update my current fuseboard (RCD and wired fuses) to an MCB type (with RCD) and add a circuit (or two) for the garden.

There is a 25 metre run from the current consumer unit to the new shed position and I would like to run an SWA cable under the new patio and path position to avoid the chance of a spade hitting it.

From the new shed position, I planned a small CU to feed a couple of indoor sockets (fridge freezer/power tools), an outdoor socket (strimmer etc), a pond pump, some (low voltage type) lights and a quartz heater.

The gazebo will be tall enough to mount a 1-2kw quartz heater in the centre of the roof leaving enough clearance. The heater will be controlled by a suitable "dimmer".

I would appreciate some advice from the group:

1. What gauge SWA should I use assuming a 16A supply over that length? 2.5 or 4mm?

1. Should I use an extra cored cable to supply the heater separately?

2. Should I supply the power from the house on the non trip side of the CU and provide the RCD function in the shed CU?

1. Should I use the house supply earth via the SWA shield or install a separate rod at the shed location?

Thanks for your help,

Colin M

[John Rumm]

According to:-

scrape in on 2.5mm sq. Myself I would use 4mm to allow for some expansion room.

You can run it from a separate MCB on the shed consumer unit if you want.

That would be best - less chance of the outdoor wiring causing unwanted trips on the house RCD.

At that distance I would lean toward a separate earth spike. You can export the house earth down the screen of a two core SWA to provide protection to the cable en route. But then terminate the cable into an insulated CU at the shed so that the earth is not connected at that end.

[Christian McArdle]

At least 4mm. If you expect to use the heater much, then 6mm, as there's no point in expensively heating the ground up with all that voltage drop.

Firstly, definitely separate earth rod and "whole shed" 30mA RCD. The best solution is RCBOs, but is well overkill.

Personally, I'd run a 32A circuit to the shed in 6mm. I'd then have the following circuits:

B6A MCB lighting B16A MCB heater B20A MCB socket circuit (radial)

Although 6mm is just OK for voltage drop over the 25m, it is actually much less of an issue, as you are unlikely to be drawing more than a couple of kW at the same time anyway, unless you mow your lawn in winter with the heater on. Even if you draw the full 32A (very unlikely), the voltage drop is still just within limits, assuming the circuit wiring is short.

Christian.

[Colin M]

I'm not sure how much the heater will be used and on what setting. TLC sell a 2kw quartz unit with what look like two separate 1kw element blocks. I may just modify the heater to switch the two 1kw blocks separately (like an old bar fire) to control the heat.

To cover every eventuality, I can use 6mm cable. I assume it's not that much harder to work with and I can easily terminate it in the CU at both ends?

OK, will add an earth rod to the spec.

Exactly my thoughts and what is on my sketch. Should I just put the water feature pump on a flexible cable with plug top or hard wire in on separate MCB and use the MCB as a switch?

Use a petrol mower, but best to plan for future use, eg electric bbq!

Colin

[Lurch]

On Wed, 30 Jun 2004 12:50:47 +0000 (UTC), "Colin M" strung together this:

Could do.

You shouldn't do this. You can wire a circuit from the CU in T&E, or whatever fixed wiring method you're using, to a DP switched fused spur and wire the pump into that. You can use the switch to turn it on and off.

[Christian McArdle]

Run it off an FCU from the socket circuit. Ensure you change the fuse for max 3A (unless it is a large fountain or something). Don't use an MCB for functional or isolation switching. It isn't suitable.

Christian.

[Colin M]

Thanks, will do. The MCB switching was just a "being lazy" suggestion!

Colin