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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Lights Dim https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1259541881 Message started by mickhock on Nov 30^th, 2009, 12:44am

Title: Lights Dim
Post by mickhock on Nov 30^th, 2009, 12:44am

I have just run power to my workshop which is no more than a 25m cable run from my main CU. The previous owner of my house had fitted a junction box in an outside toilet ready to run a cable externally to the workshop that goes back to a dedicated breaker in the main CU. As i will sometimes use the workshop as an office i've fitted a 1KW heater and will have a PC plus printer in there plus lights, i worked out i should never be using more than 2 or 3 KW. I ran 4mm cable from the junction box to the workshop and have installed a CU, however when i cabled it all up i discovered the previous owner had only run 2.5mm cable internally to the junction box in the toilet from the main CU.
When i was testing things i had a 100w bulb plugged in and switched the heater on and the bulb dimmed slightly. Surely even with 2.5mm cable it should be able to handle a 1KW heater and a 100W bulb.
Any ideas to possible problems.

Title: Re: Lights Dim
Post by Zambezi on Nov 30^th, 2009, 8:30am

You need to get a voltmeter on the cable to see how many volts are getting to your shed/office.
What size circuit breaker has been fitted in the CU for this circuit?
Is the circuit RCD protected?

Technically you should not be messing with electrics in your garden because of Part P.

Title: Re: Lights Dim
Post by mickhock on Nov 30^th, 2009, 2:06pm

Thanks for the reply.
I'm working away for a few days so can't check at present. Is it volt drop your looking for?
The circuit is RCD protected at the Main CU, i can't remember the Circuit breaker size will have to check.
I have connected the workshop supply in the workshop temporaily to a 13A socket so i could get a light working to carry out fitting walls and insulation etc. I have an extension reel plugged into this socket with the light connected to the reel and it was to this extension reel i plugged the heater into as well just to test it was working and when i did the light dimmed. The extension reel has a 13A fuse on it so no more than 13A's are flowing.

Title: Re: Lights Dim
Post by CWatters on Nov 30^th, 2009, 7:44pm

Finding it hard to work out what you have but it looks like..

CU to Loo in 2.5mm2 - How long?
+
Loo to shed in 4mm2 - 25m
+
Temporary socket
+
Extension lead of unknown wire size and length.
+
Light and heater load

Title: Re: Lights Dim
Post by mickhock on Nov 30^th, 2009, 10:15pm

CU to Loo in 2.5mm2 - How long? ..... Approx 10m
+
Loo to shed in 4mm2 - 25m ...... Approx 15m
+
Temporary socket .... 13A Plug socket
+
Extension lead of unknown wire size and length. .... B&Q extension lead approx 25m
+
Light and heater load .... 1KW heater plus 100W bulb

Now you've put it like that i may be panicking prematurely, i didn't think about the extension lead, it's probably another 25m of less than 2.5mm cable. I will connect it up properly and see how it goes.

I'll measure the voltage at the shed... what is the acceptable range.

Title: Re: Lights Dim
Post by The_Trician on Dec 1^st, 2009, 12:10am

Not much point in measuring the voltage offload.

Ideally, you want 6,00mm 3 core armoured cable all the way from your main consumer unit to the shed.

TT

Title: Re: Lights Dim
Post by CWatters on Dec 1^st, 2009, 8:48am

The eye is quite sensitive to light so quite a small sudden change is noticable. Voltage drom may not be as bad as you think.

Should still do a proper job as The_Trician suggests. I'll be doing the same job in the spring - or at least I'll be digging the trench and my electrician will be doing the hook up.

Title: Re: Lights Dim
Post by mickhock on Dec 1^st, 2009, 10:24pm

First of all apologies for time wasting. The light dimming happened last thing late on Sunday after a long day working in the shed, i was just quickly checking things. With Cwatters logical breakdown and with more time and care I've checked again.
First the volt-drop, the reading on the Main CU is 234V and is the same in the shed, my meter does not show tenths of a volt so the drop is less than a volt. The extension reel is in fact 30m and there may have been a poor connection on the 13A socket.
With it all checked over and using a block connector instead of the extension reel i did the same test and this time there was no discernable light dimming.
I should have done all this before posting.
I plan to replace the 2.5mm run in the near future anyway.
Thanks for all your comments.