goaty
|
| posted on 4/12/08 at 08:48 AM |
|
|
Electrical info
Hey,
not sure i fi in the right room but anyway.
I have just taken on a new workshop but need some light shed upon electrical systems.
I have a 3phase supply in there and currently one duoble socket single phase taken off it.
I need to add some more single phase sockets but not sure how to add them in.
Do i create a ring as per a house??
or do i just take off from the current socket and run them in series??
I ask as there is only one 3core cable going into the current socket, nothing looping back....
Can anyone help??
many thanks
|
|
|
|
|
Mr Whippy
|
| posted on 4/12/08 at 08:59 AM |
|
|
As far as I’m aware you just keep wiring the next cable into the same terminals as the last one and so on till you can’t add any more as you have
reached the maximum current capacity of the original cable. You may have to upgrade the fuse or circuit breaker
here's a guide
linky
Fame is when your old car is plastered all over the internet
|
|
|
JoelP
|
| posted on 4/12/08 at 09:06 AM |
|
|
No mr W!  Naughty advice 
A basic overview of electrical systems.
The cable is picked to supply the current required. The fuse is then picked to prevent the cable being overloaded. So the very LAST thing you want to
do is upgrade the fuse beyond the capacity of the cable! That way lies fires.
First step is to identify the cable size, and the fuse size. Typical domestic socket cables are 2.5mm and occationally (not often though) 4mm.
In a typical installation 2.5mm cables can take over 20A, sometimes up to 27A depending on route and length etc.
Assuming you want extra sockets for normal use, you have several option.
Can be done via a 32A ring in 2.5mm, or a 2.5mm radial with a 20A mcb.
If you want extra sockets for low consumption, ie computers, charges etc, then you can add a 13A fuse in something like a switched fused spur, and go
as far as you like in 2.5mm cable.
You should identify your earth supply, check it is adequate and determine if you have or want RCD protection.
This advice is only good for commercial because to do domestic wiring you need to be qualified and registered.
|
|
|
Mr Whippy
|
| posted on 4/12/08 at 09:28 AM |
|
|
quote:
Originally posted by Mr Whippy
You may have to upgrade the fuse or circuit breaker
I said you may have to upgrade the fuse...
The original fuse it could be a lot lower than the already installed cable capacity since he has only one socket currently fitted, obviously you would
not change it to being greater
[Edited on 4/12/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
|
|
|
AndyGT
|
| posted on 4/12/08 at 09:33 AM |
|
|
I was under the impression that you could only have one socket on a spur?
Plus wouldn't it be best to just make goaty's spur into a ring and thus more than doubling his final potential current and still limiting
the current on the RCD/fusebox to reduce the risk of fire?
|
|
|
JoelP
|
| posted on 4/12/08 at 09:43 AM |
|
|
quote:
Originally posted by AndyGT
I was under the impression that you could only have one socket on a spur?
if you spur it off a fuse you can go as far as you like, as current on the spur is limited to 13A. Unfused spurs are one per point, but i dont like
them as you can draw more than the current rating though a solitary double socket (26A).
[Edited on 4/12/08 by JoelP]
|
|
|
Mr Whippy
|
| posted on 4/12/08 at 10:02 AM |
|
|
quote:
Originally posted by JoelP
quote:
Originally posted by AndyGT
I was under the impression that you could only have one socket on a spur?
if you spur it off a fuse you can go as far as you like, as current on the spur is limited to 13A. Unfused spurs are one per point, but i dont like
them as you can draw more than the current rating though a solitary double socket (26A).
[Edited on 4/12/08 by JoelP]
When I wired my last garage I used cooker cable (got a reel off it for free )and ordinary 13amp sockets since I knew things like my welder,
compressor, lights etc would all be on at the same time, that’s about 14 years ago so I can't mind what the circuit breaker rating was but never
had any problems with it
Fame is when your old car is plastered all over the internet
|
|
|
JoelP
|
| posted on 4/12/08 at 10:24 AM |
|
|
6mm socket circuits are bloody hard to wire up! Thats a lot of strandage in each terminal
|
|
|
richardlee237
|
| posted on 4/12/08 at 10:27 AM |
|
|
As the supply is 3 phase then I asume that the exisitng socket is tapped off between one of the phases and neutral.
You should taken into account the current balance on the phases to ensure that your 3 phase supply is not overloaded on one phase.
By its very nature a 3 phase supply is capable of delivering large amounts of power and can do considerable damage before the fuses blow or breaker
trips.
If you do not understand 3 phase theory then you really should get in an electrician who does, it could just save your life.
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
|
|
|
nitram38
|
| posted on 4/12/08 at 11:18 AM |
|
|
First place to start is what you want to use the circuit for.
You then need to see if a radial circuit (sockets in series) or a ring circuit is better.
Cable sizes depend on length of run of the cable as well as current rating, so for longer runs you need bigger cables.
As far as I am aware the maximum rating of 2.5mm without taking account of voltdrop is 18.5A (according to table 4D2A in BS7671 regs) and not 20A as
stated.
A ring circuit has more advantages over radial circuits.
Under 17th edition regulations, all socket outlets must be rcd protected where subject to the possibilty of carelessness and not under the
maintenance of a skilled person. That means you!
An RCD alone does not give short circuit protection, only shock protection. You will need an RCBO if you want to do both or a split fuseboard which
has an RCD mainswitch.
If you employ people then Electricity at Work Regulations 1989 come into play and you will need the extended circuit tested. (Minor Electrical
Installation Works)
Even if you don't extend the circuit and employ people, you will need a Periodic Inspection Report on the entire installation.
How do I know all this? I am an electrician of 24 years experience and I am taking my 2391 testing and inspection exam today! 
[Edited on 4/12/2008 by nitram38]
|
|
|
PaulBuz
|
| posted on 4/12/08 at 12:08 PM |
|
|
quote:
Originally posted by nitram38
As far as I am aware the maximum rating of 2.5mm without taking account of voltdrop is 18.5A (according to table 4D2A in BS7671 regs) and not 20A as
stated.
Not necessarily.
It depends on the reference method of installation.
18.5 amps applies(before correction factors) only if the cable is enclosed in a conduit in a thermally insulating wall or the like.
In my experience this is unlikely in an industrial enviroment, the cable is much more likely to be clipped direct(table 4D2A refers to a multicore
cable) when the max current is 27A, or enclosed in a conduit,23A.
I'm not trying to nitpick, its just as I know you are aware there are many factors to take into account & sometimes the average Joe will
take whats written as gospel & could lead to a dangerous install.
Good luck with the exam
ATB
Paul
|
|
|
JoelP
|
| posted on 4/12/08 at 12:11 PM |
|
|
quote:
Originally posted by nitram38
As far as I am aware the maximum rating of 2.5mm without taking account of voltdrop is 18.5A (according to table 4D2A in BS7671 regs) and not 20A as
stated.
Hi martin. I only have 16th ed OSG to go by, but app6 on p120, table 6D1, allows 27A for 2.5mm cables clipped direct to a wall and not plastered in,
or 24A in surface run conduit.
Bugger, beaten to it word for word!
[Edited on 4/12/08 by JoelP]
|
|
|
nitram38
|
| posted on 4/12/08 at 01:29 PM |
|
|
He did say 3 core cable and as I can't see what he is running it in/with I went for the worst case.
Either way, he should really get someone in who knows what they are doing and do not have to ask questions!
|
|
|
AndyGT
|
| posted on 4/12/08 at 02:25 PM |
|
|
"class dismissed!!!!" 
|
|
|
JoelP
|
| posted on 4/12/08 at 02:29 PM |
|
|
quote:
Originally posted by nitram38
He did say 3 core cable and as I can't see what he is running it in/with I went for the worst case.
Either way, he should really get someone in who knows what they are doing and do not have to ask questions!
amen to that, theres no substitute for knowledge and a tester!
|
|
|
goaty
|
| posted on 5/12/08 at 07:44 AM |
|
|
thanks for all the info guys, should have it sorted out 2mo.
Going to change it from Radial to a ring to make it safer and have a deadicated isolator for my welder, should do the job.
thanks again
|
|
|
MikeRJ
|
| posted on 5/12/08 at 09:20 AM |
|
|
One thing I do know is that you must not mix phases on 13 amp sockets in the same area. With two appliances plugged into different phases you could
have 415v between them under fault conditions.
|
|
|
nitram38
|
| posted on 5/12/08 at 09:37 AM |
|
|
quote:
Originally posted by MikeRJ
One thing I do know is that you must not mix phases on 13 amp sockets in the same area. With two appliances plugged into different phases you could
have 415v between them under fault conditions.
Not true, as long as they are labelled, but bad practise
|
|
|
