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Hi all,
I’ve just completed a large house re/ new wire with new 15 circuit split MK board.
Test is fine but have low IR on some circuits, board randomly trips rcd on one side no pattern.
Its a big house lots of tech plugged in etc, so I’m thinking update from B to C type mcbs Incase it’s an inrush issue on one of the circuits but I’m open to suggestions???

Thanks .
 
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Charlie_

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Arms
Changing b to c will have no relevance to the RCD tripping.

Changing MCBs to RCBOs would make sense though.

By low IR reading, what are the actual readings?
 
  • Thread Starter Thread Starter
  • #3
Changing b to c will have no relevance to the RCD tripping.

By low IR reading, what are the actual readings?
Worst circuit was 8.8mohm on existing circuit. All others went 90 through to <999
 

Charlie_

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Arms
I take it you mean 8.8 Mohm?
That is totally fine
Do you have an earth leakage clamp?

What’s your split like on the board?
Well balanced out?
 
  • Thread Starter Thread Starter
  • #5
I take it you mean 8.8 Mohm?
That is totally fine
Do you have an earth leakage clamp?

What’s your split like on the board?
Well balanced out?
No don’t have earth leakage clamp, the board is high in Mcb ratings but fairly evenly split.
 

Charlie_

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Arms
Is it only tripping the RCD with equipment plugged into sockets?
 
  • Thread Starter Thread Starter
  • #7
Is it only tripping the RCD with equipment plugged into sockets?
It’s hard to say as they have a lot of hard wired equipment I can’t get at, boiler, fridge Frezzer, etc, I’ve told them it’s something they have connected to the circuits or plugged in that they need to eliminate
 

richy3333

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Mentor
Arms
Supporter
Esteemed
It’s hard to say as they have a lot of hard wired equipment I can’t get at, boiler, fridge Frezzer, etc, I’ve told them it’s something they have connected to the circuits or plugged in that they need to eliminate
How can you tell 'them' that when you have done little I&T to establish the fault - from what you have said so far? Possibly is an appliance or combination but more work needed to identify this?
 
  • Thread Starter Thread Starter
  • #10
Why do you think 8.8Mohm IR could be having an effect on this? Have you calculated the leakage current that will flow due to this value?
Hi, no I don’t thing it’s an issue I was just giving the details about the test. No I’ve not calculated the earth leakage, I’m fairly new to this so I know far from everything and hope to pick up on the knowledge from this forums.
 

Charlie_

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Arms
You should invest in an earth leakage clamp, most wholesalers will have them in.
You must have unplugged everything when you done your IR tests? Or that lower reading could be misleading.
 
  • Thread Starter Thread Starter
  • #12
How can you tell 'them' that when you have done little I&T to establish the fault - from what you have said so far? Possibly is an appliance or combination but more work needed to identify this?
Hi , I’ve tested the whole installation and rechecked all the fixed wiring, and found no issues.
 
  • Thread Starter Thread Starter
  • #14
You should invest in an earth leakage clamp, most wholesalers will have them in.
You must have unplugged everything when you done your IR tests? Or that lower reading could be misleading.
Yes everything was unplugged and usb built in sockets was bypassed
 

Charlie_

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Arms
So now you need to ascertain whether the problem is faulty appliances or an accumulation of earth leakage
 
  • Thread Starter Thread Starter
  • #16
So now you need to ascertain whether the problem is faulty appliances or an accumulation of earth leakage
I think it’s accumulation of earth leakage but I will get them to try to eliminate the appliances, What are my options if it is earth leakage?
 

DPG

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Arms
Esteemed
Large house with lots of tech - sounds like a perfect job for a full RCBO consumer unit to me.
 

Charlie_

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Arms
If it is earth leakage then do away with the upfront RCD and change MCBs to RCBOS
Or if you get a clamp you could possibly juggle things round in the board
 

Charlie_

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Arms
Eliminating appliances for accumulation is no good really..
You remove 1 non faulty appliance and hey presto all is ok. Replacement gets bought, plugged in and RCD trips again.
 
T

The Ghost

It would be unusual for a domestic to have inrush currents that would justify type C RCD. Also you might find it harder to meet disconnection times with a type C. If everything is unplugged does it trip? I am not sure whether you mean you re-wired the whole house or part of it? If it is a new rewire then the IR readings you are getting are unusually low for new cables installed properly.
 
T

The Ghost

Could be loose connections upstream of consumer unit. Have you done a ramp test?
 

Wilko

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Arms
Esteemed
Hi - if the IR tests are “in the meg Ohms” then it’s likely to be attached equipment. Perhaps turn everything on (plus boiler) and ramp test the tripping RCD. If it now trips below 15mA, start unplugging.
 
Hi - I second ramp test....however....one recent upgrade had the same issue, all tests ok. had customer to unplug anything not in use, tested all appliances...narrowed it down to possibly a cooker fault (still too random to actually id the fault ) new cooker, no issues. Sometimes it is not always black and white. Why not try another rcbo and move a circuit off the main RCD.
 
O

Octopus

Several things spring to mind:

That IR reading is far too low for new wire
Did you wire it or just test it
Do you know which circuit has the low reading
Why a big dual board in a new home
Have you ramp tested the rcds
Could you reconfigure the board for rcbo's
Do you have outside circuits

Etc etc
 

telectrix

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Mentor
Arms
Esteemed
Several things spring to mind:

That IR reading is far too low for new wire
Did you wire it or just test it
Do you know which circuit has the low reading
Why a big dual board in a new home
Have you ramp tested the rcds
Could you reconfigure the board for rcbo's
Do you have outside circuits

Etc etc
think OP's remit was a CU change.
 
O

Octopus

think OP's remit was a CU change.
Not how I read the opening sentence
 
This thread is a huge advert for RCBO boards
 
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