Silly Electrical Mishap!

[eveares]

So I am at my grandparents in Maidstone installing a Wireless Pyronix alarm in their bungalow.

To run power to the panel, I take a 1mm² T&E from a junction box in the loft (what is on one of the lighting circuits) to the FCU and then to the Pyronix panel.

First check for power at the panel and then do a 3 wire no-trip Zs test; So far so good.

I then move on to do an 500V IR test between L and E; turn off the circuits MCB and all lights/devices on that circuit and end up getting a very low readings around 0.05MΩ! I then get no power when I go to re-power the panel up.

Turns out the junction box in the loft what I thought was a permanent feed of the lighting circuit, was in fact the switched output that goes to all the external lights around the outside of the bungalow.

The switch that feeds that JB and thus the outside lights was On when I was doing my inital tests and Off following my IR test.

Yes you read it right, I had wired the alarm up to the switched output of the outside lights.

Lucky I have found another lighting junction box that I correctly traced back right by the one that I taped into under the fibreglass insulation that needs redoing as all the CPC's are twisted together outside the JB with no sleeving.

Regards: Elliott.

 

[ban-all-sheds]

So I am at my grandparents...

As a result of what, are you there? You haven't told us.

 

[eveares]

As a result that I am installing an alarm system for them as they want one.

I am staying over the night.

 

[winston1]

Your other mistake was using an FCU. FCUs are not used or required on lighting circuits. There will be no discrimination between a 3 amp fuse and 6amp MCB in the CU.

 

[eveares]

Mistake using an FCU?

My old house (wired to 16th ed) what was a new build had the alarm protected by a FCU fed from one of the lighting circuits.

Also the FCU allows one to isolate the panel from the lighting circuit.

 

[bernardgreen]

Your other mistake was using an FCU. FCUs are not used or required on lighting circuits.

No Winston1 this mistake is yours, FCUs can be used on lighting circuits for isolation of sections so that a fault in an "at risk" fitting will not put the entire lighting ciruit out of action

An "at risk" fitting could be an out door lamp or a lamp in the ceiling under a wet room or one of several other locations

 

[ban-all-sheds]

Your other mistake was using an FCU.

It was not a mistake. Please stop this. DON'T give out false information, it just confuses people.

FCUs are not used

Yes they are. Please stop this. DON'T give out false information, it just confuses people.

or required on lighting circuits.

People may require them if they wish. Please stop this. DON'T give out false information, it just confuses people.

 

[John D v2.0]

It's depressing that even a funny story immediately turns into an argument.

 

[winston1]

Definitely no need for an FCU on a lighting circuit. If isolation is wanted (also not required) a simple switch will do. The purpose of an FCU is to protect the cable which is already done via the MCB in the CU.
Would you also advocate changing all your light switches to FCUs?
What happens in the majority of other countries where FCUs are neither available nor complient?

 

[davelx]

Definitely no need for an FCU on a lighting circuit. If isolation is wanted (also not required) a simple switch will do. The purpose of an FCU is to protect the cable which is already done via the MCB in the CU.
Would you also advocate changing all your light switches to FCUs?
What happens in the majority of other countries where FCUs are neither available nor complient?

You seem not to understand the difference between something not being required and something not being permitted.

You correctly say that FCUs are not required on lighting circuits. However, they are not prohibited and if they are the most convenient way to provide isolation where desired (again, isolation may not be required by the regs, but it is not prohibited to provide it), then there is nothing incorrect about fitting them. It's much more likely for someone to have an FCU in the bits box than a suitable double pole switch. Perhaps you should look up the word "pragmatic" in the dictionary?

 

[bernardgreen]

If isolation is wanted (also not required) a simple switch will do.

Winston, please stop giving bad advice........

A simple switch will NOT provide isolation. Anyone could flick the switch back on, which if someone else was working on the defective lamp, could be very hazardous.. With an FCU the fuse can be removed ensuring that accidental restoration is most unlikely to happen.

Isolation can be required, the alternative could be darkness until an electrician can disconnect the faulty item to allow MCB and / or RCD to be reset.

 

[jg321]

If isolation is wanted (also not required) a simple switch will do.

Whether or not you believe isolation is necessary, do you honestly, hand on your heart, believe that it's a good idea to have a switch to isolate an alarm panel?

 

[John D v2.0]

Whether or not you believe isolation is necessary, do you honestly, hand on your heart, believe that it's a good idea to have a switch to isolate an alarm panel?

Of course, same goes for boilers. Technically with all these things you can isolate at the cu, but if they're on the lighting circuit that's not ideal.
Any half decent alarm can't be silenced by turning off its power supply so that's no issue. In fact many work the other way round, going off automatically if the mains is absent for too long.

 

[Deleted member 18243]

As a result that I am installing an alarm system for them as they want one.

I am staying over the night.

You started your post with the word "so", as if you were following on from something you'd written previously!

 

[eveares]

I vacate this thread for a single day, and it explodes all over the issue of FCU's on a lighting circuit!

Any half decent alarm can't be silenced by turning off its power supply so that's no issue.

I think you may have missed the point; it is not about the alarm being silenced by switching the mains power off, but rather that one may isolate it accidentally with a normal switch and risk having the alarm go off when the backup battery gets low and eventually fail when the batteries fully drain.

A simple switch will NOT provide isolation. Anyone could flick the switch back on

Quite so.

but if they're on the lighting circuit that's not ideal.

But you will likley notice if your lighting circuit has no power and thus alert you to an issue.


Lastly as quoted from the installation manual:


"Ensure that a readily accessible disconnect device Incorporated in the premises installation wiring shall be provided external to the equipment with a contact separation of at least 3,0mm and connected as closely as possible to the supply. "