GFCI's and RCD's

[vwes59]

I'm sure this is something that someone has come across, but anyhow.

Been asked to install an inflatable hot tub for a client. They already have a summerhouse with its own CU which is connected back to the house via a 6mm SWA to a Henley block tapped off the incoming tails. There is an RCD in place to protect a 6A lighting circuit and a 10A radial.

I plan to put in a 20A MCB for the inflatable hot tub and an external socket. The max draw the tub will do is 2.5kW and that's with the heater and jets working.

Now here's the thing. Like with all inflatable hot tubs, this comes with a power cable with an integrated GFCI. I want to be really cautious where water is concerned, but I've heard tails that these GFCI's sometimes do not play nice with the RCD's in the CU's and can give nuisance tripping when there is in fact no fault. (I believe GFCI's are rated at 5ms as opposed to RCD's which are at 30ms).

Anyone installed this kind of thing, and have you used the supplied cable with the GFCI, or replaced it with a bog standard cable, letting the RCD in the CU do the protection ?

 

[DPG]

I'm sure this is something that someone has come across, but anyhow.

Been asked to install an inflatable hot tub for a client. They already have a summerhouse with its own CU which is connected back to the house via a 6mm SWA to a Henley block tapped off the incoming tails. There is an RCD in place to protect a 6A lighting circuit and a 10A radial.

I plan to put in a 20A MCB for the inflatable hot tub and an external socket. The max draw the tub will do is 2.5kW and that's with the heater and jets working.

Now here's the thing. Like with all inflatable hot tubs, this comes with a power cable with an integrated GFCI. I want to be really cautious where water is concerned, but I've heard tails that these GFCI's sometimes do not play nice with the RCD's in the CU's and can give nuisance tripping when there is in fact no fault. (I believe GFCI's are rated at 5ms as opposed to RCD's which are at 30ms).

Anyone installed this kind of thing, and have you used the supplied cable with the GFCI, or replaced it with a bog standard cable, letting the RCD in the CU do the protection ?

They often have a 10mA RCD rather than a 30mA one. I think that is what you mean.

And GFCI is a US term for an RCD.

 

[pc1966]

You won't get selectivity between a 30mA supply RCD and a 10mA hot-tub one (as above, GFCI is the USA term for RCD).

But they don't cause problems, except some will trip both with you press the 'test' button as they actually divert current to the CPC, rather than bypassing the sense coil on one side to simulate a fault imbalance.