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3 wire systems: are they still allowed?


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Hi All.

I am sure this has been asked before, but I seem to be having trouble locating any info.

A long time ago everyone down my way and probably other places to, were installing panels that could be run of a 3 wire system. (both the sounders and the detection sharing the neutral).

I stopped doing this years ago but I have a client that I do a lot servicing for, yet another engineer does the installs and he is still using this 3 wire method.

I am pretty sure the regs changed with the introduction of EN54, but I cant find any text to back this up.
I would like to point this out to my client and if necessary ad it to my reports.

Would anybody have any knowledge on this.

Today I telephoned: FIA, BAFE, Elesca, FPA, TBFC, NICEIC and not one person could help.

I have seen the text somewhere but cant for the life of me remember where.

Many Thanks


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Thanks Tom for getting back to me.

Voltage would be around 27.6 volts, which is pretty standard for most panels.
no problems getting FP200 3core and earth, it is mostly used for these instals or repair work including additional items added to an existing installation.

I used to use it myself a long time ago. but I am sure something changed, something to do with EN54 & LPCB but I have not been able to find anything.
Even the tech department at C-tec panels don't recommend using it, even though their panels where and still are capable of 3 wire installs.


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I tried surfing the web and the only bite I had was about 2 or 4 wire systems and the only 3 wire systems were 240 VAC which is definitely not acceptable. I checked out BS EN 54 but as there are at least 31 parts so I chose not to study it to far and LPCB proved unfruitful. This level on technicality is far beyond me but I would suggest you try http://firealarmengineers.com/forum/or you could try http://electrical.theiet.org/index.cfm who may be able to help but at least they will be talking your language.

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Eddy I have been asking around and a few points were raised, the terminology, the supply to the Control Indicating Equipment (CIE) is 240VAC therefore the conductors should be termed live, neutral and earth, from the CIE to the zones is 24 VDC therefore the term is positive and negative and maybe this could have caused some confusion.

Some have said they do not see any reason why a common negative wire could be used but why, unless you can purchase fire resistant cable with only three conductors. If you can buy FR two core cable and four core cable why do you need three core? The only time you may need three core is if it is an old installation using three core system and it needs an extension or repair without replacing the whole system.

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