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Mixed Wiring

Former Community Member over 4 years ago

We have been invited to tender for the rewire of lighting and power to a government building.
The single compartment trunkings carry recently installed ELV cabling consisting of fire alarm and general alarm cabling. We have been asked to replace the existing LV singles.
Existing services to the ceilings means there is no capacity left to install new containment and would almost be impossible to install.
To install the LV wiring would depart from BS7671 528.1 / 515.2 / 528.3 along with BS5839 and BS8519
7671 states ‘Any intended departure from these Parts requires special consideration by the designer of the installation and shall be recorded on the appropriate electrical certification specified in Part 6. The resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations.’
Since there is no design or intervention by any electrical consultants I would assume we become the designers simply by installing the cables into the trunkings and terminating into the various items of equipment.
As a result I wouldn’t say that the resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations is met, as stated above.
Is just merely noting the departure on the EIC sufficient or should I be looking for some form of written agreement that the installation will not comply with current standards.

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0 Former Community Member over 4 years ago

Good morning all and thank you for your responses.
In answer to you reply’s:
Yes there was mixed wiring contained with the trunkings before the fire and as Alcomax states the circuits were isolated and disconnected. In theory the fire alarm and alarm companies have not made any variations by installing their cabling into trunkings filled with unused ‘dead’ cables.
Installing additional containment is pretty much out of the question with the existing services installed.
Yes agreed the FP200, although mains rated, is still a problem with 5839. There has been a case where mains and fire alarm cables have been installed in the same containment and when testing commences the fire panel lights up like a Christmas tree…. Just one example. As Alan mentions these issues may well appear after later after completion.
As QS I’d be a lot more comfortable with a piece of paper with someone’s signature confirming it’s fine to proceed.
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0 Former Community Member over 4 years ago

Good morning all and thank you for your responses.
In answer to you reply’s:
Yes there was mixed wiring contained with the trunkings before the fire and as Alcomax states the circuits were isolated and disconnected. In theory the fire alarm and alarm companies have not made any variations by installing their cabling into trunkings filled with unused ‘dead’ cables.
Installing additional containment is pretty much out of the question with the existing services installed.
Yes agreed the FP200, although mains rated, is still a problem with 5839. There has been a case where mains and fire alarm cables have been installed in the same containment and when testing commences the fire panel lights up like a Christmas tree…. Just one example. As Alan mentions these issues may well appear after later after completion.
As QS I’d be a lot more comfortable with a piece of paper with someone’s signature confirming it’s fine to proceed.
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Mixed Wiring

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