Hey Bruce, ring wiring

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panel. In other

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I believe ring circuits connect to a single 30 or 32A breaker with wire rated significantly lower than 30A.

I would think a ring circuit would be considered conductors in parallel, which is not generally allowed by the NEC for conductors smaller than

1/0 (310.4). And one of the conditions is that parallel wires are equal length.

I agree that the wire gauge couldn't be reduced under the NEC.

You don't actually double the wire current capacity in a ring circuit because the length of wire on each side of the ring is not equal (except at the midpoint) so the current does not equally split.

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Running it in a loop is not a violation of the US National Electric Code but what would be a violation would be to connect both ends to separate breakers as I believe is done in United Kingdom ring mains. You also could not connect them to a breaker that is of greater ampacity then the one allowed in the code for a single conductor of that same gauge. What you end up with is a ring main with none of it's advantages and all of it's extra work and additional materials.

-- Tom Horne

panel. In other

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easier to terminate.

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reference is in the

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Yes. (32A nowadays)

Rated for at least 2/3rds of the 32A. In practice, in most cases the wire is rated a good deal more than this minimum as it's not usually installed in the worst possible scenarios.

A ring circuit can supply any number of socket outlets. It is recommended (although not a strict regulatory requirement) that a single ring circuit is limited to supplying the socket outlets to no more than 100m^2 of floor area. A single ring circuit can provide up to 7.2kW. If the designer knows that more power than this will be required in a particular area, then they should reduce the floor area supplied by a single ring circuit and install more of them. This is normally only an issue in commercial/industrial areas, not residential where 7.2kW per

100m^2 is more than enough. A ring circuit must not be used to power electric heaters which form the primary building or water heating systems. They can be used for supplementary heating and small (single basin) water heaters.

Indeed. Designers should avoid designing a ring which might have maximum load drawn in just a small part near one end.

No, both ends go to the same fuse/breaker

It's now known as IEC 60309-2.

There is something similar in the US now, but the current ratings are different. Don't know if it comes under IEC 60309-2 or some other standard.

There's a limit to the circuit fusing though. The 16A BS4343 must not be connected to a circuit fused at more than 20A in UK. That's because the plug isn't fused. (I don't remember off the top of my head the max limits for the higher current BS4343 sockets.)

A 16A BS4343 socket is allowed on a 32A ring circuit providing an additional fuse or breaker (up to 16A) is fitted for the 16A BS4343 socket. This is quite unusual though.

This is rather more related to the circuit fusing than the circuit topology. We also have 20A and 32A radial circuits in the UK, and these still require fused plugs, because protection at 20A or 32A is too high for safety of the appliance flexs.