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Topic Title: Max disconnection time for a 30mA RCD
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Created On: 23 July 2007 12:18 PM
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 23 July 2007 12:18 PM
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Smith249

Posts: 359
Joined: 09 September 2004

Guys,

Whats the max disconection time, I've got a brandnew MK 30mA RCD which is tripping at 71mS but I thought the max was 41?

Thanks.
 23 July 2007 12:22 PM
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deapea

Posts: 369
Joined: 13 May 2007

200ms at rated trip current
40ms at 500%
 23 July 2007 12:23 PM
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rocknroll

Posts: 8824
Joined: 03 October 2005

For BSEN 61008

1/2 In - No trip
100% In - 300ms
500% In - 40ms

What are you testing it at?

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leave nothing but footprints!"
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"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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 23 July 2007 04:25 PM
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ebee

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Joined: 02 December 2004

Rock,
Don`t forget the old BS was 200mS and then there`s delayed RCDs to consider as well

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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 23 July 2007 05:07 PM
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rocknroll

Posts: 8824
Joined: 03 October 2005

OP says he just purchased it new so its unlikely to be BS 4293

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 23 July 2007 05:19 PM
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ebee

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Good point Rock.

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Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 23 July 2007 05:52 PM
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deapea

Posts: 369
Joined: 13 May 2007

What was the reason for increasing the trip time from 200ms to 300ms. Is to do with nuisance tripping? I don't know the answer but there must be some logical reason.
 23 July 2007 05:58 PM
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MrP

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deapea
The tripping time didn't increase! different standards BS-EN shutting the shop off home

MrP
 23 July 2007 06:10 PM
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deapea

Posts: 369
Joined: 13 May 2007

Thanks Mr.P.
If a an rcd is used as supplimentary protection against indirect contact it must trip in 40ms at 500% of rated trip current(150mA). Now I always found this pretty straight fwd to remember because if 30mA is 200ms then x5 of rated current would be a fith of the trip time, hence the 40ms.
Now this logic doesn't follow for a 300ms rcd. Am I being too simplistic?
 23 July 2007 11:47 PM
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AJJewsbury

Posts: 11251
Joined: 13 August 2003

What was the reason for increasing the trip time from 200ms to 300ms.

And the daft thing is that as BS7671 moves closer to Harmonized standards, some disconnection times (if the DPC is to be believed) are going to change from 0.4s to 0.2s (i.e. 200ms) (e.g. for TT final circuits) - thus an BS EN RCD as 1x rated current will no longer be sufficient, whereas a good old BS one would have been fine!
- Andy.
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