Odd test results on RCD Spur

[haptism]

Tested an RCD spur earlier with some odd results

Tested at x 1/2 (both waveforms) and no trip
x 1 (0 degrees = 28.5 ms), (180 degrees = 18.4 ms)
x 5 (0 degrees = 8.2 ms), (180 degrees = 40 ms)

S0 getting bang on 40ms at x5 on 180 waveform; i know its in limit but was expecting it to be (at least) as low as the x5 0 degrees result.

The supply is TNCS, the circuit has low Zs, testing carried out at rcd spur itself, with load side disconnected. Tried it with two different sets of leads and same result, the testers been recently calibrated.

What would you do in this situation ?? I realise the x5 result is within limits (just). Really im perplexed, if this result is due to the nature of the waveform, or if the RCD is iffy.

And to add to the mix im reading that x5 rcd tests are , strictly speaking only required where your max Zs values cannot be met.. e.g. TT installations.

 

[Pete999]

Tested an RCD spur earlier with some odd results

Tested at x 1/2 (both waveforms) and no trip
x 1 (0 degrees = 28.5 ms), (180 degrees = 18.4 ms)
x 5 (0 degrees = 8.2 ms), (180 degrees = 40 ms)

S0 getting bang on 40ms at x5 on 180 waveform; i know its in limit but was expecting it to be (at least) as low as the x5 0 degrees result.

The supply is TNCS, the circuit has low Zs, testing carried out at rcd spur itself, at load side with circuit disconnected. Tried it with two different sets of leads and same result, the testers been recently calibrated.

What would you do in this situation ?? I realise the x5 result is within limits (just). Really im perplexed, if this result is due to the nature of the waveform, or if the RCD is iffy.

And to add to the mix im reading that x5 rcd tests are , strictly speaking only required where your max Zs values cannot be met.. e.g. TT installations.

How many times did you carry out the tests? could be just a glitch

 

[haptism]

How many times did you carry out the tests? could be just a glitch

At least 4 times, twice with each set of leads

 

[Pete999]

At least 4 times, twice with each set of leads

Oh right thanks need to think again.

 

[diditrain]

Was there any load connected?

 

[haptism]

Was there any load connected?

No, load was disconnected

 

[diditrain]

Was it new or an old one with a sticky switch?

 

[haptism]

Was it new or an old one with a sticky switch?

Its a brand new one out the box,

 

[Ian1981]

5x rcd tests on 30mA rcd’s are for the circuits circuits requiring and covered by said rcd and require additional protection so must trip within 40mS @ 150mA regardless of what type of earthing arrangement is in place.

 

[haptism]

5x rcd tests on 30mA rcd’s are for the circuits circuits requiring and covered by said rcd and require additional protection so must trip within 40mS @ 150mA regardless of what type of earthing arrangement is in place.

Yeh additional protection against direct contact , x1 tripping times below 200ms would account for that where the circuit has a low enough ZS would it not ? I know the regs state x5 have to be within 40ms for TN systems too, but thats' backup to protect against a low high Zs scenario aint it

 

[static zap]

What band RCD ?

 

[haptism]

What band RCD ?

Gotta admit its a Toolstation jobbie, SafetySure brand

 

[Pete999]

What band RCD ?

Oh BRAND I did wonder

 

[static zap]

Oh BRAND I did wonder

Oops , Pink Floyd !

 

[haptism]

Oh Band, its a usual AC band/type

 

[static zap]

You got it right ,the first time ... (not looking at screen /typing too fast)
-- Sorry me bad--

 

[Ian1981]

Yeh additional protection against direct contact , x1 tripping times below 200ms would account for that where the circuit has a low enough ZS would it not ? I know the regs state x5 have to be within 40ms for TN systems too, but thats' backup to protect against a low high Zs scenario aint it

It’s got Nothing to do with back up of anything or a high zs.
A 100ma rcd would be suitable for a high zs on a TT for fault protection for circuits where additional protection is not required however it’s not a requirement to test a 100mA rcd at 5 x the rated current as it does not afford additional protection.
Only a 30mA rcd will offer additional protection and 40ms is the time given before an electric shock could become fatal.
Hence at 150mA it must disconnect in 40ms or less
Bs en 61008 rcds for 30mA
1x test for fault protection, must disconnect in 300ms or less
5x test for additional protection, must disconnect in 40ms or less

 

[sparksfly]

It passes....but ...only last Saturday I had to return to a job I had installed sockets on TT using a safetysure FCU...it had only lasted 2 years. Not fitting that again, they are a good price for a reason ...it will be a power breaker now.

 

[Grezza]

I’d replace. Never had a brand new trip that slow when tested so likely an early fault. Just swap it and sleep easy

 

[haptism]

1x test for fault protection, must disconnect in 300ms or less
5x test for additional protection, must disconnect in 40ms or less

Aw right, will have to get my head round that, nice one. Where I was going with ZS scenario sounded right in my mind but hey ho potatas/potatoes , u learn something new every day

 

[Simonslimline]

What has Zs

Aw right, will have to get my head round that, nice one. Where I was going with ZS scenario sounded right in my mind but hey ho potatas/potatoes , u learn something new every day

Will an MCB operate at 30ma!

The RCD is being used for additional shock protection due to failure of basic protection/carelessness of user etc. it should operate before the end user receives a fatal shock.

The MCB offers protection to the cable.

 

[static zap]

( Was beginning to wonder if weirdness was a feature of supply,(and suggest testing elsewhere))
Finger points at shabby product ,nearly good enough !

 

[haptism]

What has Zs


Will an MCB operate at 30ma!

The RCD is being used for additional shock protection due to failure of basic protection/carelessness of user etc. it should operate before the end user receives a fatal shock.

The MCB offers protection to the cable.

Yes when you put it like that it all makes sense now. Feel rather sheepish now tbh to have made such a daft assumption. I mean the ZS itself wont affect the trip time will it . Will be reading up again on this subject and nail it.

 

[haptism]

Just to update, rcd was replaced today with the Power Breaker brand and all tests out as it should.