How to carry out RCD test for shower?

[nazoom]

Hi

My exam is coming soon and I have a question.
My installation is single phase , TN-S. There is a shower unit protected by the RCD. My questions are:
Do I carry out RCD test at the RCD itself in the C/U or do it at the shower unit itself? If at the shower unit where does the tests leads go?

Many Thanks.

 

[wallyanker]

Do the tests at the CU

 

[D Skelton]

Which exam are you on about out of interest?

 

[nazoom]

Fault finding and testing for Periodic Inspection and testing.

Thanks.

 

[D Skelton]

Ah, ok. You can carry out the test at the CU. Line lead to 'line out' on RCD (bottom left), neutral lead to 'neutral out' on RCD (bottom right) and earth lead to earth bar.

Edit: Presuming that it's a normal RCD

 

[nazoom]

So there is no need to do RCD test on the shower unit itself? Yes the RCD is normal.

Many thanks.

 

[D Skelton]

No, the clue is in the title

It's called an RCD test, not a shower and RCD test.

Happy to help

 

[sparky-s-w]

what about an RCD trip time test, that would have to be done at the shower isolator no

 

[somersetsparks]

No all rcd tests should be done at CU with loads disconnected.

 

[Guest55]

Bang on ^^^^

 

[topquark]

To complete the picture you're testing the RCD only with this test (that's why it's with loads disconnected, so you can be sure that only the trip current from the meter is being used to trigger the RCD). The Zs (in combination with the other tests) of all the other circuits being within spec is sufficient proof that the RCD will work for the circuits routed through it.

 

[sparky-s-w]

ok, but why then is the RCD trip results on an EIC on every circuit, why not just have one box for the entire cert, or 2 boxes x1 & x5

 

[somersetsparks]

Becuase you may have all rcbo's with different test results.

 

[sparky-s-w]

right got ya, should have thougt of that, ill shut up now.

 

[topquark]

ok, but why then is the RCD trip results on an EIC on every circuit, why not just have one box for the entire cert, or 2 boxes x1 & x5

A good question, I'll pass on that one, that's a question for the form designer.

For an RCD (as opposed to RCBO) I use two separate lines on the form and record the times for x1 x5 at both 0 and 180 for posterity (one line for 0deg and one for 180deg).

If you did test the RCD from each circuit, you would actually get slightly different timings for each point/circuit tested (because of the EFLI from that point on the circuit being different for a radial for example).

The maximum Zs values have been worked out to ensure that sufficient fault current can flow to cause the device to trip. You can see the advantage, it's easier to do at the CU; you need to reset the RCD for each test (5 tests, 4 trips, 5 resets). The more modern tests have an auto mode making it even easier. Imagine the situation if you were trying to test the upstairs lighting circuit. You'd be up and down stairs a lot if working alone on it.

It will be the same if you are ever asked to "ramp test" an RCD or RCBO, you do it at the device. HTH.