SPD2

Jonny72 · Sep 10, 2024

Ok need advice.

Two domestic consumer units both fed of same Escos ideally should only have been one but she to it being an older house and the location of DNO equipment this was not possible without unreasonable expense. As both are beside each other and fed from same Escos could 1 SPD 2 in one consumer unit service the circuits on both boards???

Any help be appreciated.

J

Avo Mk8 · Sep 10, 2024

What is the total length of cable between Lin at the isolator of the non-SPD board, via the SPD in the other board, to earth?
It's supposed to be less than 50cm.
I suspect your suggestion might result in less protection for the second board.

mainline · Sep 10, 2024

Jonny72 said:
Ok need advice.

Two domestic consumer units both fed of same Escos ideally should only have been one but she to it being an older house and the location of DNO equipment this was not possible without unreasonable expense. As both are beside each other and fed from same Escos could 1 SPD 2 in one consumer unit service the circuits on both boards???

Any help be appreciated.

J

One spd should benefit both.

Jonny72 · Sep 10, 2024

Avo Mk8 said:
What is the total length of cable between Lin at the isolator of the non-SPD board, via the SPD in the other board, to earth?
It's supposed to be less than 50cm.
I suspect your suggestion might result in less protection for the second board.

The boards are literally beside each other. Maybe a difference of 10/15 cm tails from same Henley Blocks. DNO is NIE (Northern Ireland) wanted to charge 300 quid to move the meter and head.

Jonny72 · Sep 10, 2024

mainline said:
One spd should benefit both.

Thanks. My thoughts process was it's same as on a single board All circuits connected by bus bar and some further away from SPD Just wanted to check to make sure there was nothing obvious that I wasn't aware or had thought of. Thanks.

Avo Mk8 · Wednesday at 12:41 PM

Jonny72 said:
The boards are literally beside each other. Maybe a difference of 10/15 cm tails from same Henley Blocks.

Just to emphasise the 50cm 'rule' I was talking about, some theory below. A surge is shunted to earth, so the length of the earth connection used is part of the calculation. So distance of Lin of second CU to Lin of first CU (if that's where the SPD is going), plus distance from Lin to MCB protecting SPD, plus distance MCB out to SPD, plus distance from SPD earth terminal to main earth bond. All those added together is supposed to be less than 50cm, and if it is that, the household could still get a 500V surge on top of the mains voltage (strictly on top of the SPD cut-in voltage)!

https://www.electrical-installation.org/enwiki/Connection_of_Surge_Protection_Device#Examples_of_good_and_bad_SPD_installations

mainline · Wednesday at 1:58 PM

Avo Mk8 said:
Just to emphasise the 50cm 'rule' I was talking about, some theory below. A surge is shunted to earth, so the length of the earth connection used is part of the calculation. So distance of Lin of second CU to Lin of first CU (if that's where the SPD is going), plus distance from Lin to MCB protecting SPD, plus distance MCB out to SPD, plus distance from SPD earth terminal to main earth bond. All those added together is supposed to be less than 50cm, and if it is that, the household could still get a 500V surge on top of the mains voltage (strictly on top of the SPD cut-in voltage)!

https://www.electrical-installation.org/enwiki/Connection_of_Surge_Protection_Device#Examples_of_good_and_bad_SPD_installations

View attachment 118111