Discuss RCBO 5In trip times. in the Electrical Forum area at ElectriciansForums.net

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Just installing a new consumer unit for a customer. Split load board with 1 half RCD & the other half RCBO's. RCD & all but 1 RCBO has had good trip times, all sub 40ms at 1In & 5In, but the 6A RCBO for the kitchen lighting circuit is tripping at 40.8ms & 40.7ms at 5In. If I disconnect the outgoing live & retest the the trip times are 18.5 & 17.2. Anyone shed any light as to why this is happening & is it acceptable to test the RCBO without the outgoing ways connected?
 
........ is it acceptable to test the RCBO without the outgoing ways connected?

Yes , and its the prefered method anyway.
Theres a good chance electronic transformers / ballasts are buggering up the readings at the first attempt at testing so youre good to go with recording the 18 / 17 ms trip times
 
Biff/Somerset..Why ? Where is this written I can't say I have seen this anywhere although granted I don't own every GN book published, this is a serious question not a dig.
J
 
Biff/Somerset..Why ? Where is this written I can't say I have seen this anywhere although granted I don't own every GN book published, this is a serious question not a dig.
J

No probs with asking jimmy lol.
The rcd manufacturers recommend testing of the devices in this way for a start.
Plus the test is just to acertain the trip time of the rcd , so theres no need for any other part of circuit to be connected.
And finally , electronic gizmo's can interfere with the readings , as shown by ste macs query.
 
Sounds like a bad earth on the kitchen lighting circuit to me.

Am not sure why you are disconnecting the lighting circuit to test the RCBO. I thought you had to measure disconnection times from the furthest point ( if not every point) on the circuit, so as to test the cabling of the entire circuit, and not simply the RCBO on it's own.

Or am I missing something?
 
Sounds like a bad earth on the kitchen lighting circuit to me.

Am not sure why you are disconnecting the lighting circuit to test the RCBO. I thought you had to measure disconnection times from the furthest point ( if not every point) on the circuit, so as to test the cabling of the entire circuit, and not simply the RCBO on it's own.

Or am I missing something?

Er no.
Why test through loads of cable / switches / fittings which can lead to inaccuracies when you can just do it at the CU ?
Have a read of my post #5 for more info.
 
Surely if you test at the CU you will get a perfect reading every time?

If you test at the end of the circuit you will ensure a) the earth is continuous and b)the EFLI is low enough to operate the device in the required time.

Am not sure why you would want to ensure that the RCBO is fine, whilst the circuit and accessories that the device is meant to protect may harbour a fault that causes the (perfectly fine) RCBO not to operate in the required time?

I am not trying to be confrontational, I am simply confused as this is the first time I have encountered this method of recording trip times. I always record from the end of line.......
 
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Surely if you test at the CU you will get a perfect reading every time? Only if the rcd is functioning correctly , if its not then it wont pass the test no matter where you do the test.

If you test at the end of the circuit you will ensure a) the earth is continuous and the EFLI is low enough to operate the device in the required time. Eh ? this is a rcd test , what EFLI got to do with it ? that test is done seperately ?

Am not sure why you would want to ensure that the RCBO is fine, whilst the circuit and accessories that the device is meant to protect may harbour a fault that causes the (perfectly fine) RCBO not to operate in the required time? Then you have a problem with the wiring or accessories , not with the rcd , and you would need to investigate this seperately - your confusing what the test is for to be honest and the rcd is there to protect the user / occupier not the accessories.

I am not trying to be confrontational, I am simply confused as this is the first time I have encountered this method of recording trip times. I always record from the end of line.......

.......................
 
P.S. If the device is operating correctly with no circuit connected, but fails to operate in the required time with the circuit connected, the device has become pointless...Why have disconnection device that doesn't disconnect (in the real world) ?

I would check the earthing of this circuit again.
 
As a path for current leakage, which would imbalance the coil. A high impedance on this path (or no path) would reduce ( or negate) the ability of the device to operate in the required time.

No?
 
Surely if you test at the CU you will get a perfect reading every time?

If you test at the end of the circuit you will ensure a) the earth is continuous and b)the EFLI is low enough to operate the device in the required time.

Am not sure why you would want to ensure that the RCBO is fine, whilst the circuit and accessories that the device is meant to protect may harbour a fault that causes the (perfectly fine) RCBO not to operate in the required time?

I am not trying to be confrontational, I am simply confused as this is the first time I have encountered this method of recording trip times. I always record from the end of line.......

I agree most of these regs are ambiguous,its good to question a lot of things as it shows we are thinking and not following like sheep but testing at the farthest point is not necessary.Quote from wiring matters Spring 2010 "Whether the RCD in question protects a number of circuits,eg on a split load board,or an RCBO is used to protect a single circuit,or an RCD is installed nearer the item of equipment being it is protecting,the tests can be carried out immediately on the load side of the device.Often it is suggested that an RCD protected circuit should be tested at the extremity,ie. at the same point at which the Zs measurement is taken.There is LITTLE TO BE GAINED in testing the RCD at the extremity of the circuit it is protecting.Firstly , the test is required to prove the RCD operates correctly.As the circuit in question will meet all other requirements ie earth loop impedance and volt drop,add little to the operating time of the device" Hope this helps.
 

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