ChrisW
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| posted on 7/12/10 at 12:37 PM |
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Need more capacity in consumer unit
I want to fit a dedicated 16A feed for my compressor in the garage. Normally I'd just run a cable, put a 16A plug on the wall, and wire to a
spare slot on the consumer unit (also in the garage, so easy to do).
But, there's no space left in the unit to fit another switch.
What's the 'correct' way to solve this? I'd like to avoid changing the whole consumer unit if at all possible. Is it
acceptable to fit a second board (say something like THIS) and spur it off the output
from the main switch in the existing board?
Chris
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MikeR
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| posted on 7/12/10 at 12:44 PM |
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correct way is to bend over and pay a spark to do it for you!
its more than a minor change and therefore you've got all the part 'p' stuff to worry about.
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blakep82
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| posted on 7/12/10 at 12:45 PM |
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^ correct. but when i wired in my compressor i needed a 32a circuit, and only had 16a cabling to the garage. me and my dad rewired the whole thing.
shhhhhh 
when we had the bathroom done last year, the electrician but a standalone circuit breaker thingy next to our old fuse box (old fashioned style) so i
guess it can be done, just as long as the total consumption isn't more than the cable going to the consumer unit you have currently
[Edited on 7/12/10 by blakep82]
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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BenB
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| posted on 7/12/10 at 12:59 PM |
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As long as you don't overload the main switch you'll be okay. Mind you the main switches are sometimes a bit marginal in terms of amps-
they're usually 100A which isn't that much by the time you've got a few ring circuits, a freezer, a hob, an oven etc etc. I know
diversity will knock it down but equally I know a big old compressor and a big old welder in a garage can pull the amps quite nicely....
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cliftyhanger
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| posted on 7/12/10 at 01:04 PM |
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Years ago (so may not be current regs, excuse the pun, but did pass inspection 2 years ago) a sparky added a 2nd consumer unit in a rented house. He
used a connector block on the main power cables from the meter to the consumer unit
http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Connector_Blocks/index.html
and then to the 2 consumer units.
Trouble is you will need to pull the fuse, but when mine was inspected the chap just fitted a new seal, no questions asked. (I did all the works
before it was all outlawed. Honest. And none has failed inspection. The stuff I didn't do needed some minor tweeks)
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cliftyhanger
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| posted on 7/12/10 at 01:08 PM |
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quote:
Originally posted by BenB
As long as you don't overload the main switch you'll be okay. Mind you the main switches are sometimes a bit marginal in terms of amps-
they're usually 100A which isn't that much by the time you've got a few ring circuits, a freezer, a hob, an oven etc etc. I know
diversity will knock it down but equally I know a big old compressor and a big old welder in a garage can pull the amps quite nicely....
I wouldn't worry. I have been doing some work at a bedsit house (loathesome places, but it is paying work )
That has 100A incomer. 8 bedsits, each with own 13A baby belling cooker, 2KW heater, 2KW water heater plus 8 kettles and all the other stuff
bedsitters have. And one electric shower in the place. (other is a gas powered bathroom with a multipoint) All runs with no issues, passed inspection
with some minor issues a few weeks ago.
The same owner has another similar setup with 2 electric showers, and 11 bedsits. All off 100A incomer.
So I doubt a normal house will suffer any issues............
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daniel mason
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| posted on 7/12/10 at 02:20 PM |
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how many lighting circuits do you have? if you have multiple circuits and not much load on them (less that 1200 watts) you could theoretically double
them up,put them on a 10 amp mcb which would free up a circuit in your fuse board!
you shouldnt really be doing it yourself though
if your loaded up then you will have to split the tails in a 100 amp tail block and (1 wire in from fuse and 1 wire out to each fuse board) so you
are not spurring off your main switch! you are doing it directly from a 100 amp suply
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MikeR
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| posted on 7/12/10 at 02:33 PM |
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Just because the incoming cables are rated to 100amps - don't expect the fuse to be 100amps. When i had my meter replaced by the electricity
company (20 years is the limit before they need replacing apparently) he refused to fit a 100amp fuse. Said standard building practice now was to fit
80 amp. If i wanted 100amp i'd have to get them back out and prove it was blowing the 80amp fuse legitimately.
Not had a problem with the 80 amp fuse (but do want to upgrade the garage to 40 amp supply soon so i may have some interesting conversations ahead of
me).
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dan__wright
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| posted on 7/12/10 at 03:33 PM |
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that will be fine, i had to do this in one of my server rooms as we had filled the board, additional consumer unit and tapped it from the main
isolator on the first board.
as for 100a main fuse, even if it has a 100a label it might not be 100a, one of our new building, 3ph 100a, checked draw and well under 100a, fired
new kit up and pop, when the fuses were checked they were a mix of 80 and 60 but labeled 100
[Edited on 7/12/10 by dan__wright]
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JoelP
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| posted on 7/12/10 at 06:22 PM |
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daniel certainly has the easiest solution so far, and its quite acceptable in theory.
The correct way to add another board is via the henley blocks linked above, to split the tails outside the existing CU. Spurring of the main switch
isnt good because you cannot get the correct sized conductors in - the new board might be mini but it still needs correct sized conductors.
Id look at re-arranging the existing myself, if not lights than maybe another - post a photo if you want advise.
[Edited on 7/12/10 by JoelP]
second edit, lots of main fuses are only 60A. Ive never seen one pop in normal use. In fact i was at a house wired wrongly via a 45A fuse and that
never popped, powering a full big house with electric shower, ceramic hob, double oven, electric plinth heater, and the usual 2 rings/lights etc. So i
myself never worry about the fuse popping.
[Edited on 7/12/10 by JoelP]
Beware! Bourettes is binfectious.
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daniel mason
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| posted on 7/12/10 at 09:53 PM |
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you would need to be running a lot more than 60 amps and for a long period of time to blow a 1361 fuse by overload. am a trained electrician and if
you have 25 mm incoming tails (the norm for a 100 amp suply) yo cant just try to squeeze another cable into the input of the main switch!!! as joel
says the connection will be poor.
you can get a 100 amp link for a fuse board but these take up another way which is not an option as yours is already full. really does amaze me what
people are prepared to do even though they know the danger.
the size of your main fuse is not really the issue as long as you use the correct size cable to suit. remember the fuse protects the cable so you dont
want to run 10mm tails on a 100 amp fuse as the cable could melt before the fuse blows.
split the tails outside the fuse board in a tail block to feed a seperate small unit!
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slingshot2000
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| posted on 8/12/10 at 12:23 AM |
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Chris,
I am very concerned about your knowledge of electrics, and just as much concerned as to some of the advice you are being given on here with regards to
something that could kill you and anybody else (friends,children, family) .
By what you say, you are obviously not an electrician!
Please be careful
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ChrisW
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| posted on 8/12/10 at 01:50 AM |
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Hi All
Thanks for the advice everyone. To clarify, my question was really 'what's the acceptable way to do it from a building regs point of
view' rather than 'how do I do it'. I can think of severals ways of achieving what I want, I just wanted to know which way the
regulations would recommend.
I had thought of 'doubling up' the lighting circuits, but the MCB's for the lighting circuits are all 5A or thereabouts (less than I
need anyway).
The board itself is obscure in that the modules are a funny size, so switching them would be difficult - I've never seen this size on sale
anywhere. It might be possible to trim the front casing slightly to make a standard size module fit - I need to look in to that - as I'm pretty
sure it's standard DIN rail behind. I'll have to isolate the power and remove a module to check this though and havn't got around
to it yet.
The outputs from the main switch look large enough to take another set of conductors but again I'd need to take it apart to have a proper look.
From what I can see without probing too deep (ie without turning the power off) it's got a flat bus bar type arrangement in it, but the
connectors are twice the thickness of the bar. I'd only be putting a cable capable of 16A in, and the run will be about 6-7m, so nothing too
thick.
In terms of current, it's a 100A fuse on the meter and an 80A main switch if I recall correctly. We do pull a fair bit though. Luckily the
showers are fed from the boiler, but we do have an electric oven (hob is gas), and a hot tub which pulls 32A on full blast. However it's
unlikely the compressor would be on at the same time as the tub which means it drops to 16A for just the heater, and that's on a thermostat.
quote:
Originally posted by slingshot2000
I am very concerned about your knowledge of electrics, ..... By what you say, you are obviously not an electrician! Please be careful
All paper qualifications I have are low voltage stuff - ie electronics! However, my Grandfather was an electrician and I took great influence from
him from a very young age and was able to 'wire things up' as soon as I was old enough to hold a screwdriver. I helped my father re-wire
our house when I was 8 although I seem to recall I did most of the actual wiring, he just pulled the cables in... although he did get my Grandfather
in to check everything before it was switched on! I worked in event lighting for a few years in my late teens dealing with big three-phase rigs, but
that was before any of this part P stuff came in. Even now, my day job also requires me to deal with three phase installations, standby systems,
UPS's, etc, although usually just making sure contractors are doing things the way I ask.
Cutting a long story short, I'd describe myself to be competent but not qualified.
Thanks for your concern though - glad to know you lot do appreciate me!
Cheers, Chris
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