Earth loop values

Gnasher · May 18, 2009

Here we go for my first post.

I have been working as an electricien for 25 years

This may cause some discussion?

With reference to Earth loop values in the Bible.
Has any one ever contacted the manufacturer of MCB’s to enquire to the specific loop values they publish? You may be surprised to find that they are higher values than the Bible.
Now the question is can you go by these values.

Spudnik · May 18, 2009

Hi Steve and welcome.

Good question, one of which like you say, may cause a few heads to hurt.

Typically, as you know, manufacturers instructions generally over rule the BRB, however im not sure on technical details over ruling.

Would be interesting to hear what others opinions are.

Guest123 · May 18, 2009

Hey Steve, welcome along.

Personally I go by the BRB as on the forms it asks for max permitted by BS 7671 not by Merlin or Hager or Wylex etc.

Also if the book values are lower then that can only be a good thing surely.

[ElectriciansForums.net] Earth loop values

P.S I have my tin hat on!!!!

Gnasher · May 18, 2009

Quite right lenny however if the disconection times are achieved with higher Loop readings can this not prevent a lot of costs especially on periodic's if this was noted on the report.
As for new works this should be designed in with Ze in mind.

I like the one's that make you think.

Guest123 · May 19, 2009

Hi.

Agreed, on new installations there is no excuse for failing to comply with max values for Zs as full consideration should have been given in the design stage.

I see what your saying with regard to the periodic on an existing installation scenario, but again I'm drawn to the whole "to BS7671" quote. Worst case scenario would be having to change an MCB for an RCBO. Agreed, there is extra cost involved but I think it would niggle away at me if I didn't because the Zs still complied with manufacturers spec.

It's a tough call but I would deffo advise the client on addtional RCD/RCBO protection if the Zs fell outside of BS7671 values on an existing installation.

Cheers.