Dual rcd board tt system

[dnjr]

Dear all
Wonder if anyone can enlighten me
I've just changed a board to a dual rcd board. TT system with ze of 100 ohms
All circuits test ok and everything fine for 2 days . Had a call to say that while the customer was out ( so nothing in use) both rcds tripped at same time , they know this as two timer clocks ( one on each rcd side stopped at same time)
As far as I know it's only happened one , customer has asks what would cause it and I don't know so thought I would ask. I'm guessing it's something external but would appreciate anyone who can enlighten me
Cheers


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[HandySparks]

Had a call to say that while the customer was out ( so nothing in use) both rcds tripped at same time , they know this as two timer clocks ( one on each rcd side stopped at same time)

Just because the customer was out, doesn't mean that nothing was 'in use'. At the very least there were two clocks!

Central heating (incl water heating), fridge and freezer are an obvious starting point.

 

[Octopus]

Just because the customer was out, doesn't mean that nothing was 'in use'. At the very least there were two clocks!

Central heating (incl water heating), fridge and freezer are an obvious starting point.

tripping both rcds?

Has the OP got a earth clamp meter? Thats where I would start!

 

[dnjr]

Just because the customer was out, doesn't mean that nothing was 'in use'. At the very least there were two clocks!

Central heating (incl water heating), fridge and freezer are an obvious starting point.

Hi handy sparks. Thanks for the reply
Boiler switches off at 9 and rcds tripped at 10.30 so can't be that, fridge and freezer are on same circuit so only one rcd would trip. Just very strange they both went at same time
There is a time clock on each circuit but them both to fault at same time would be amazing . More chance of England winning euros I would think


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[dnjr]

tripping both rcds?

Has the OP got a earth clamp meter? Thats where I would start!

Hi Murdoch. Yep have a clamp meter / tong type , not been asked to go back as yet as its only tripped once. They asked me why it would happen , I'm not too sure so thought I would ask those more learned than myself.


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[Octopus]

TBH you need to ask them to keep a note of when it happens - it could be a one off, if could be a supplier issue, any thunder & lightening?

 

[dnjr]

Hi murdoch. Have already asked them to keep a log. Man of the house is onto it, said he had a notebook that would be just the job. No thunder or lightning or local road works etc.. Thanks for replies watch this space..


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[telectrix]

could be due to these:

 

[Octopus]

Did you put a 100mA or 30mA time delay in place of the 100A isolator?

 

[dnjr]

Did you put a 100mA or 30mA time delay in place of the 100A isolator?

Standard dual 30mA rcd board with 100A main switch. Not much experience of TT systems. Wrong ?


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[Octopus]

Standard dual 30mA rcd board with 100A main switch. Not much experience of TT systems. Wrong ?


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Not wrong, I haven't done an AMD3 CU TT change since the metal boards came about so I was just wondering whether you had fitted the RCD in place of the isolator.

This isn't a trick question or point BTW

I've got a TT CU change to do soon so just wondering what other people do!

I fit RCBO boards normally so I will need to change the 100A isolator for a RCD to achieve DP isolation

 

[dnjr]

Phew. I'm almost a TT virgin so was worried I'd missed something. Cheers


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[Midwest]

Would only need up front s type, if the installation has a distribution circuit, simple tails and and bespoke gland would suffice, I believe. As regards fault youve had, read here loads of different possibilities. Might be some paths for you to follow, if you search below.

 

[123]

How do you know it tripped at 10.30?

 

[123]

Not wrong, I haven't done an AMD3 CU TT change since the metal boards came about so I was just wondering whether you had fitted the RCD in place of the isolator.

This isn't a trick question or point BTW

I've got a TT CU change to do soon so just wondering what other people do!

I fit RCBO boards normally so I will need to change the 100A isolator for a RCD to achieve DP isolation

Just out of curiousity will you be using RCBO's on that board change? If Single Pole Solid Neutral ones, an N-E fault would take out the time delay RCD

 

[dnjr]

How do you know it tripped at 10.30?

Both time clocks stopped at same time


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[dnjr]

Dear all
Wonder if anyone can enlighten me
I've just changed a board to a dual rcd board. TT system with ze of 100 ohms
All circuits test ok and everything fine for 2 days . Had a call to say that while the customer was out ( so nothing in use) both rcds tripped at same time , they know this as two timer clocks ( one on each rcd side stopped at same time)
As far as I know it's only happened one , customer has asks what would cause it and I don't know so thought I would ask. I'm guessing it's something external but would appreciate anyone who can enlighten me
Cheers


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Dear all
Just thought I would update this one
Surprise suprise. Owner had done sone diy after I left and borrowed a neutral for his garage lighting so when turned on a light inside it tripped both rcds. Gota love em. Cheers for replies

 

[Leesparkykent]

Phew. I'm almost a TT virgin so was worried I'd missed something. Cheers


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Ideally there should be an up front 100mA S type RCD to provide fault protection for the links between the main switch and RCD's.

 

[dnjr]

Hi lee. I though s type were not intended for Personal shock protection as they are slower to react and could allow current to flow for an unacceptable period of time. Is this not the case ?

 

[Leesparkykent]

will still provide fault protection through ADS and protection against the risk of fire. Just not suitable for the requirements of additional protection. Your scenario is described on page 20 of the on site guide.