wiring in a 3KW kiln

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wrote:

Don't RCD a kiln. They have high leakage currents. A 100mA split-load CU is OK, but 30mA and a fused outlet is asking for nuisance triggering.
I'd fit a fused spur from a convenient supply, then an unfused industrial plug and socket (the round blue ones). I'm no expert on kilns, but I've had plenty of trouble with welders in the past. Domestic-grade 13A plugtops and sockets just don't like passing 13A for long periods. -- Smert' spamionam
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Andy Dingley wrote:

Whenever our neighbour is out welding his old car that he's doing up, all the lights in our house flicker considerably
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I'm actually in the Republic of Ireland, slightly different wiring regulations apply however re: the 3KW kiln I would suggest the following:
Treat it like any electric oven. Ideally, if it's in an outbuilding you need to consult an electrician as the earthing arrangements would need to be checked over and you could find yourself in SERIOUS trouble if you create a TT supply in the outbuilding.
As for wiring it up generally:
16A RCD on the board. Radial circuit to: 20A or 45A Double pole switch and connector unit located near the kiln.
BS1363 should definitely not be used as a connector for sustained 3KW loads.
Blue CEE-17 (Industrial) plugs 16A would work fine. These provide a much better connection surface on the pins and in the socket than BS1363.
On a modern plug-in kiln the leakage currents shouldn't be large enough to trip the RCD but it is possible and was definitely a problem with older cookers etc.
Bear in mind it's prob. designed to be plugged in to a European 16A Schuko (CEE 7/7) socket so should work perfectly well on a 16A radial circuit with RCD. VDE/Schuko (CEE 7/7) plugs/sockets tend to be far better at handling sustained 3KW currents without over heating.
Schuko sockets are recessed and thus do not need to have the pins sheathed (you physically can't touch them while inserting the plug) this allows for a MUCH greater contact area on the pins meaning they run cooler.
BS1363 plugs and sockets only make contact with the area around the pin tip due to the sheathing and so as not to expose the user to live metal as they're inserting the plug
There's also the added problem of the fuse holder.. Which tends to heat up again due to the very small contact area.. This varies depending on the manufacturer. Hence you should always use high quality plugs (e.g. MK) on heavy appliences.
In general BS1363 plugs are designed for switched 3KW loads, not continious ones.
On 12/01/2004 14:45, in article btubsk$86q$ snipped-for-privacy@yarrow.open.ac.uk, "R W"

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wrote:

I would suggest the following:
- Put in a proper power feed to a consumer unit in the outbuilding using SWA cable of appropriate rating. For example, you might want a total of 32A for everything in the outbuilding. You would protect the SWA cable and everything downstream with a 32A MCB in the main house consumer unit or install a separate MCB switch if preferred.
- If the building is some way from the house, the outbuilding should be treated as a TT system of its own and an earth rod and 100mA time delay RCD used in that consumer unit. For short distances from the house you can export the house earth, but it is not a preferred approach.
- In the consumer unit of the outbuilding, put in at least one 6A breaker for the lights. You don't want them going off if there is an RCD trip so they/it should be upstream of any RCD.
- For other power in the outbuilding, you should have RCD protection. Either you can create a split load CU where the breakers between the main switch and the RCD are not protected and those downstream are; or you can use individual RCBOs (RCD + MCB together basically).
- For general power, you could create a ring circuit protected at up to 32A and wired in 2.5mm^2 cable or a radial circuit with daisy chained sockets in the same size cable protected with a 16A breaker.
- For the kiln, an EN 60309 16A blue industrial connector would be the best choice. This should be wired specifically to its own RCD protected or RCBO breaker in the outbuilding CU.
.andy
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You haven't given enough information, like how the outbuilding is supplied and if it has a consumer unit or distribution board, and what sort of earthing your system is.
I would install a dedicated circuit with 16A MCB protection. I would make the connection to the kiln using an unfused double pole switch connection unit, wired direct with no plug+socket.

I would not RCD protect a Kiln. The element is likely to leak anyway which could cause tripping when first switched on after a period of non-use, but a non-portable appliance of this type does not present a significant electric shock hazard if the installation's earthing is correctly installed. However, this means it should not be connected via a socket outlet in an outbuilding as the socket could easily be used to power a portable appliance.
The circuit might need RCD protection against a high earth fault loop impedance. This would require details of your earthing system, and how the outbuilding is connected to the supply (including cable type and length) in order to determine if such RCD protection is required.
--
Andrew Gabriel

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