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Discuss RCD disconnection times! in the Electrical Forum area at ElectriciansForums.net

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Hi all, just a quick one regarding RCD disconnection times.

So for non rcd protected circuits disconnection times of 0.4 / 5 seconds and 0.2 / 1 second for TN + TT final and distribution circuits.

RCDs (fire / fault protection) usually 300ms at rcd for rated current. (differs when s type).

So if I'm using an RCD in a TT system for fault protection due to high Zs readings am I to use the 300ms of the above OR use the 200ms for the TT?

And then what would I record on the test sheet as there's only one rcd test result box? Would it be the X1 for fault protection or the X5 for the additional protection? I think naturally I would put both down to prove both functions were operating in time.

I know it'll be a very simple answer but I'm just overlooking it. I don't have any books to hand at the minute as I'm out the country but it's one that just crossed my mind.

Thanks.
 

Mike Johnson

-
Esteemed
Arms
You mean you have gone away and did not take your OSG with you. 😆

Lots of variables to take into account for a simple answer, BS number, circuit breaker type, rating and how high the Zs is?

Don't overthink this enjoy your holiday and just drink more.
 
You use 0.2sec. On the schedule you record ×5 for 30ma devices (the fact this is for additional protection isn't really relevant as the device will also provide fault protection), anything above 30ma you record ×1.
 
You mean you have gone away and did not take your OSG with you. 😆

Lots of variables to take into account for a simple answer, BS number, circuit breaker type, rating and how high the Zs is?

Don't overthink this enjoy your holiday and just drink more.
Haha!

It was more just a simple example, so say I had a zs of 85 ohms, which is obviously too high for fault protection from a bs 60898.. So I'd use the 61008 of a split load board say to protect for fault current.

So if I got 250ms trip time for the 61008 at rated current would that be OK. I'm inclined to say it would as its below the recommended 300ms at rated current given in the table (forgot table number) but its just thrown me off a little with an mcb or non rcd protected circuit being 0.2s?

Im actually working on a vessel in Taiwan haha, I wish i was in holiday and drinking beer!! Cheers.
 
You use 0.2sec. On the schedule you record ×5 for 30ma devices (the fact this is for additional protection isn't really relevant as the device will also provide fault protection), anything above 30ma you record ×1.
That answers my question. Perfect thanks for that westward10!

Explains it all perfectly. I was just a bit q confused as it says 300ms for RCDs at rated current or 0.2 in TT systems.

Is that because its the lesser of the two figures (0.2 and 300ms?)

So a TN system is 0.4s but rated current of RCDs are 300ms.. Use the 300ms as its the lesser?

Thanks again
 
That question has made me see my fault.

I've got it from the rcd trip times. I was using the x1 figures of 300ms.

If an rcd was used for fault protection (for example 100ma at rated current would be 300ms trip time)?

So if I'm using 30ma RCDs regardless wether it's for fault or additional it would be x5 and 40ms.

If I was using anything other than 30ma it would be x1 and 0.4 for TN systems and 0.2 for TT systems?
 
A 30ma device to EN61008 or EN61009 should trip within 300ms at ×1. If these are being used for fault protection then they must disconnect within 200ms for TT. So regardless if for fault and/or additional a 30ma device should trip at 200ms or less for ×1 and 40ms or less for ×5. You will only record ×5 however as this is the prevalent measurement.
 
A 30ma device to EN61008 or EN61009 should trip within 300ms at ×1. If these are being used for fault protection then they must disconnect within 200ms for TT. So regardless if for fault and/or additional a 30ma device should trip at 200ms or less for ×1 and 40ms or less for ×5. You will only record ×5 however as this is the prevalent measurement.
Yeah, that's how I thought it was but went about explaining it the very long way. Thanks for your time. 👍
 

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