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economy 7


paul b b

Question

Hello guys,

looking at my first economy7 job and have a question or two about it.

The main system is a TT so should it have its own earth rod or connect the 2 cu's MET together?

If i connect them together should the Ze be taken at the economy7 cu.

Is it ok, for the purpose of doing a rcd trip time, to change the 20 dp switch to a socket?

thanks

paul

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6 answers to this question

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You should only really have one MET and if you have multiple CU's then maybe you need an external MET that all the rods/bonding connects to and all the CU's are linked to.

Ian.

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Hello guys,

looking at my first economy7 job and have a question or two about it.

The main system is a TT so should it have its own earth rod or connect the 2 cu's MET together?

If i connect them together should the Ze be taken at the economy7 cu.

Is it ok, for the purpose of doing a rcd trip time, to change the 20 dp switch to a socket?

thanks

paul

there is usually be one rod, but if there are more, they must be connected together and linked to both CU's

Ze is taken at rod only, disconnected from both CU's

you can do RCD times at the CU with probes direct to RCD. sometimes a little awkward holding all probes into place, but easier than changing a DP switch to a socket

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thanks chaps

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Personally I would always test the rcd operation from the furthest point of the circuit (where you got the highest R1+R2 reading) to prove the operation in worst case. Testing on the outgoing side of the rcd only shows the operation of the device and is disregarding the circuit.

Drop the 20A DP forward and use probes onto the terminals to test, GS38 leads only have 2mm/4mm exposed and careful use should avoid shorting out anything

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Personally I would always test the rcd operation from the furthest point of the circuit (where you got the highest R1+R2 reading) to prove the operation in worst case. Testing on the outgoing side of the rcd only shows the operation of the device and is disregarding the circuit.

Drop the 20A DP forward and use probes onto the terminals to test, GS38 leads only have 2mm/4mm exposed and careful use should avoid shorting out anything

i agree it should be tested in worst case, but the big red comic says otherwise (but still nothing to stop you testing at the end or more convenient point)

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You can use the existing Earth conductor from the Rod providing everything is in order in its installation and effectivness etc. The C.U. end of the cable should be terminated in a standard MET connection strip unit and seperate Earth conductors taken from here to the existing and the new C.U. The Ze should be taken at your new E7 C.U it will be termed Zdb and you will enter it on your EIC.Do the trip times at the RCd..or if your preference is at the D.P switch simply go across its terminals...Hope your not installing too many heaters cos sometimes they can cause problems with nuisance tripping the RCd when they all switch on together from cold.

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