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Ask The Trades › DIY Forum › Electrical Questions › Testing RCD trips MCB

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Testing RCD trips MCB (Read 7391 times)

veeves Junior Member Offline Not fried myself yet but may drown Posts: 7 Total Thanks: 0 For This Post: 0	Testing RCD trips MCB Feb 20^th, 2005, 10:30pm Hi, I have an RCD socket, wired as a spur from the main ring. When I press the test button on the RCD, it works ok for a few times, but then trips the MCB. I have nothing plugged into the RCD socket, so there is no load. Any ideas? ???
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LSpark

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Re: Testing RCD trips MCB
Reply #1 - Feb 21^st, 2005, 12:06am

Hello Veeves

You're problem sounds strange to me, pressing the 'T' or 'Test' button on the RCD, should not trip you're MCB..

Not sure what else to add, could be that it just happened the same time as another fault on the ring, or that the SRCD (Socket Outlet Incorporating Residual Current Device) is fault...

May I ask why if it work's first time, do you proceed to test again?, nothing wrong with testing, but trying to build up a picture of what's happening Undecided

« Last Edit: Feb 21^st, 2005, 12:08am by LSpark »

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veeves

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Re: Testing RCD trips MCB
Reply #2 - Feb 21^st, 2005, 5:42pm

When I first set it up, it tripped the first time I pressed the test button, but could not find anything wrong. This is why on subsequent tests I've pressed 'T' a few times. I forgot to say that its the 'Earth fault' that trips. I am going to call in a qualified electrician to sort it (I have disconnected it for the moment), but am curious as to what I may have done wrong. I've checked all the wiring and am pretty sure its all correct (including the earth).

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Lectrician Administrator Trade Member Author Offline Ask The Trades Posts: 8815 Total Thanks: 109 For This Post: 0 Braunton, North Devon United Kingdom Gender: Trade: Electrician	Re: Testing RCD trips MCB Reply #3 - Feb 21^st, 2005, 5:53pm Your MCB isn't an RCBO is it?? Does the MCB also have a small (often tiny) test button aswell?? What make is the Consumer Unit and MCB??
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veeves

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Re: Testing RCD trips MCB
Reply #4 - Feb 21^st, 2005, 6:08pm

yes it does have a test button, dont know the make I will check later. Sorry but getting confused about the difference between MCB and consumer unit, and dont know what RCBO is (hence me calling an electrician!) but am still interested to know.

Could it be that the earth fault tripping is correct when I press T on the RCD socket, does the test actually simulate an earth fault, thus the main unit thinking there is one?

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zambezi GDPR opt-out Total Thanks: 0 For This Post: 0	Re: Testing RCD trips MCB Reply #5 - Feb 21^st, 2005, 6:10pm Sounds like that is the case (if I have understood your explanation correctly)
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Lectrician Administrator Trade Member Author Offline Ask The Trades Posts: 8815 Total Thanks: 109 For This Post: 0 Braunton, North Devon United Kingdom Gender: Trade: Electrician	Re: Testing RCD trips MCB Reply #6 - Feb 21^st, 2005, 7:01pm What does the device that trips in the CU look like? How wide approx? Does it have a test button? What does it say on the device? Sounds as if you have an RCD or RCBO in the CU already, and this could protect a standard socket (ie, no need for an RCD socket outlet.)
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veeves Junior Member Offline Not fried myself yet but may drown Posts: 7 Total Thanks: 0 For This Post: 0	Re: Testing RCD trips MCB Reply #7 - Feb 21^st, 2005, 8:41pm Its a Crabtree model SB6000 RCCB, about a foot wide, with an 'Earth Fault Trip' - which is what trips when I test the RCD. So I guess this is correct then, in that it should trip when I press test? If so, funny that it does not happen consistently every time I press it?
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Lectrician

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Re: Testing RCD trips MCB
Reply #8 - Feb 21^st, 2005, 8:53pm

That sounds like the RCD (also known as an RCCB in the older days).

This will protect several (or all) of your MCB's (of fuses) in the CU.

I guess your RCCB is rated at 30mA (0.03amp). The socket will be rated at this also. Manufacturing processes will determine which trips first. If they both have a similar trip time, it could be either or both that trip.

You could do away with the RCD socket and replace with a standard socket if you so-wish.

foot wide?? The whole CU I hope - not just the trip Grin

« Last Edit: Feb 21^st, 2005, 8:53pm by Lectrician »

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veeves Junior Member Offline Not fried myself yet but may drown Posts: 7 Total Thanks: 0 For This Post: 0	Re: Testing RCD trips MCB Reply #9 - Feb 21^st, 2005, 9:31pm I see now. Yes the whole CU is a foot!!! Thanks for the advice.
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LSpark Global Moderator Trade Member Author Offline Posts: 8069 Total Thanks: 3 For This Post: 0 London, UK United Kingdom Gender: Trade: Electrician	Re: Testing RCD trips MCB Reply #10 - Feb 22^nd, 2005, 1:05am Foot wide, thought I was seeing thing's for a minute lol Quote: That sounds like the RCD (also known as an RCCB in the older days They have actualy stuck with RCCB lecc, weird I know, but true..
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zambezi GDPR opt-out Total Thanks: 3 For This Post: 0	Re: Testing RCD trips MCB Reply #11 - Feb 22^nd, 2005, 8:46pm Quote:That sounds like the RCD (also known as an RCCB in the older days They have actualy stuck with RCCB lecc, weird I know, but true.. That is so 15th edition!!
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LSpark Global Moderator Trade Member Author Offline Posts: 8069 Total Thanks: 3 For This Post: 0 London, UK United Kingdom Gender: Trade: Electrician	Re: Testing RCD trips MCB Reply #12 - Feb 23^rd, 2005, 12:30am Shuddup
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mark Junior Member Offline I love YaBB 1G - SP1! Posts: 19 Total Thanks: 0 For This Post: 0	Re: Testing RCD trips MCB Reply #13 - Mar 6^th, 2005, 9:33pm i have a double pole crabtree here in front of me (not wired up) when i switch down the RCD switch the circuit breaker switch also switches down automatically so it looks like that when the RCD part operates then the circuit breaker side also operates
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ban-all-sheds GDPR opt-out Total Thanks: 0 For This Post: 0	Re: Testing RCD trips MCB Reply #14 - Mar 6^th, 2005, 10:51pm That'll be how it interrupts the supply in the event of an earth fault...
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