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Default Wiring for a Shed

A friend has build a fairly elaborate shed - about 5m x 5m, insulated.
An electrician has installed a 63A feed from the main supply, using a
consumer unit and an MCB, to the shed (which is 75m from the house),
terminated with a 13A socket, with lighting spurred off the socket.

He's asked me to help him install 6 double sockets and wiring/switching
to 4 x 4' 50W LED batten lights.

I'm not sure yet whether I'm going to do it - I'd do it for myself, but
he's quite impatient, and I don't think he'd be happy with the 3 months
I'd give myself to exercise excessive caution. Anyway, a couple of Qs:

1) Would you use a consumer unit in the shed? If so, what's the MCB and
RCD situation? I's assume the CU and MCB/RCD arrangements at the main
supply have some bearing on this.

2) Ring or radial for the sockets? I've had a look at the DIY wiki:
http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners
I think it's going to need a ring because he's factoring in an oven
(3kW, for pottery) at a later date. But it'd be a lot easier to do a
dedicated oven socket on a separate feed from however (1) is organised,
and a radial for the remaining 5 sockets. I don't follow where the '20A'
in the radial comes from in the wiki diagram - how is a radial socket
circuit designed for a particular use? The only anticipated high current
device is a 2kW heater. But I'd guess contingencies have to be designed in.

3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?

The fact that I'm asking these questions tends towards telling him to
get an electrician - I can see this being a bit of a nightmare. But
answers will help me understand it all better, and give him something to
think about.

--
Cheers, Rob
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Default Wiring for a Shed

On 02/01/2019 21:05, RJH wrote:

3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?


Yes - there's the fill factor:

https://www.rm-electrical.com/wp-con...Technical1.pdf


That's purely on space. In essence, if it fits easily, it's OK.


Are you proposing to use singles?

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Default Wiring for a Shed

On 02/01/2019 22:14, Tim Watts wrote:
On 02/01/2019 21:05, RJH wrote:

3) Routing the wiring. He's intending to use 20mm plastic tube
conduit, which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?


Yes - there's the fill factor:

https://www.rm-electrical.com/wp-con...Technical1.pdf


Excellent, thanks.


That's purely on space. In essence, if it fits easily, it's OK.


Are you proposing to use singles?


As in a single run of cable? I need to draw it all out, but at the very
least there'll be the 13A socket and the lighting cable running through
the conduit, to keep things neat.

The lighting cable could in theory be quite skinny - 3A, for the 160W load?

--
Cheers, Rob
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Default Wiring for a Shed

On Wednesday, 2 January 2019 21:05:07 UTC, RJH wrote:

A friend has build a fairly elaborate shed - about 5m x 5m, insulated.
An electrician has installed a 63A feed from the main supply, using a
consumer unit and an MCB, to the shed (which is 75m from the house),
terminated with a 13A socket, with lighting spurred off the socket.

He's asked me to help him install 6 double sockets and wiring/switching
to 4 x 4' 50W LED batten lights.

I'm not sure yet whether I'm going to do it - I'd do it for myself, but
he's quite impatient, and I don't think he'd be happy with the 3 months
I'd give myself to exercise excessive caution. Anyway, a couple of Qs:

1) Would you use a consumer unit in the shed? If so, what's the MCB and
RCD situation? I's assume the CU and MCB/RCD arrangements at the main
supply have some bearing on this.


You'll want a local earth rod with everything RCDed.


2) Ring or radial for the sockets? I've had a look at the DIY wiki:
http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners
I think it's going to need a ring because he's factoring in an oven
(3kW, for pottery) at a later date. But it'd be a lot easier to do a
dedicated oven socket on a separate feed from however (1) is organised,
and a radial for the remaining 5 sockets. I don't follow where the '20A'
in the radial comes from in the wiki diagram - how is a radial socket
circuit designed for a particular use? The only anticipated high current
device is a 2kW heater. But I'd guess contingencies have to be designed in.


Ring has 2 slight advantages over radial: usually a mite cheaper on cable & a bit safer. But either works fine.


3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?


see the wiki page on Cable.

The fact that I'm asking these questions tends towards telling him to
get an electrician - I can see this being a bit of a nightmare. But
answers will help me understand it all better, and give him something to
think about.


Should be no nightmares once you've found out what to do.


NT
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Default Wiring for a Shed

On 02/01/2019 22:37, wrote:
On Wednesday, 2 January 2019 21:05:07 UTC, RJH wrote:

A friend has build a fairly elaborate shed - about 5m x 5m, insulated.
An electrician has installed a 63A feed from the main supply, using a
consumer unit and an MCB, to the shed (which is 75m from the house),
terminated with a 13A socket, with lighting spurred off the socket.

He's asked me to help him install 6 double sockets and wiring/switching
to 4 x 4' 50W LED batten lights.

I'm not sure yet whether I'm going to do it - I'd do it for myself, but
he's quite impatient, and I don't think he'd be happy with the 3 months
I'd give myself to exercise excessive caution. Anyway, a couple of Qs:

1) Would you use a consumer unit in the shed? If so, what's the MCB and
RCD situation? I's assume the CU and MCB/RCD arrangements at the main
supply have some bearing on this.


You'll want a local earth rod with everything RCDed.


Thanks. I'm loosely assuming there's a local earth rod fitted by the
sparks - but will check.

2) Ring or radial for the sockets? I've had a look at the DIY wiki:
http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners
I think it's going to need a ring because he's factoring in an oven
(3kW, for pottery) at a later date. But it'd be a lot easier to do a
dedicated oven socket on a separate feed from however (1) is organised,
and a radial for the remaining 5 sockets. I don't follow where the '20A'
in the radial comes from in the wiki diagram - how is a radial socket
circuit designed for a particular use? The only anticipated high current
device is a 2kW heater. But I'd guess contingencies have to be designed in.


Ring has 2 slight advantages over radial: usually a mite cheaper on cable & a bit safer. But either works fine.


3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?


see the wiki page on Cable.


Thanks - got that now.

The fact that I'm asking these questions tends towards telling him to
get an electrician - I can see this being a bit of a nightmare. But
answers will help me understand it all better, and give him something to
think about.


Should be no nightmares once you've found out what to do.


It's more the 'client' - he's quite impatient and has a habit of looking
for fault when it isn't necessarily there. A sort of irritatingly
enquiring mind looking for shortcuts.


--
Cheers, Rob


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Default Wiring for a Shed

On 02/01/2019 21:05, RJH wrote:

A friend has build a fairly elaborate shed - about 5m x 5m, insulated.
An electrician has installed a 63A feed from the main supply, using a
consumer unit and an MCB, to the shed (which is 75m from the house),
terminated with a 13A socket, with lighting spurred off the socket.

He's asked me to help him install 6 double sockets and wiring/switching
to 4 x 4' 50W LED batten lights.

I'm not sure yet whether I'm going to do it - I'd do it for myself, but
he's quite impatient, and I don't think he'd be happy with the 3 months
I'd give myself to exercise excessive caution. Anyway, a couple of Qs:


Well if you take it step by step, this is quite doable. The hard work
part is usually getting the submain there in the first place, and that
bit has been done.

1) Would you use a consumer unit in the shed?


In this case, definitely.

If so, what's the MCB and
RCD situation? I's assume the CU and MCB/RCD arrangements at the main
supply have some bearing on this.


Yup they do, you will need to find out how that end is configured since
it will limit what you can do later.

2) Ring or radial for the sockets?


32A Ring probably

I've had a look at the DIY wiki:
http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners


If you have read through of :

http://wiki.diyfaq.org.uk/index.php/...ricity_outside

its a bit more focussed on the particular job in hand.

I think it's going to need a ring because he's factoring in an oven
(3kW, for pottery) at a later date.


I would tend to lay on a dedicated radial for the kiln (especially as
many are 3kW)

But it'd be a lot easier to do a
dedicated oven socket on a separate feed from however (1) is organised,


Yup

and a radial for the remaining 5 sockets. I don't follow where the '20A'
in the radial comes from in the wiki diagram - how is a radial socket
circuit designed for a particular use?


A radial socket circuit is just a general purpose socket circuit, so it
needs overload protection provided at the origin of the circuit by a MCB
(or RCBO). The 20A comes from the size of MCB typically used if the
circuit is wired entirely in 2.5mm^2 T&E (its maximum current rating os
less than 32A so would not have overload protection with the normal 32A
MCB used on a ring). You can however wire a radial in 4.00mm^2 T&E and
use a 32A MCB if you prefer (rarely seen in practice since wiring in the
larger cable is harder work than having the extra return cable in the
smaller size for a full ring).

The only anticipated high current
device is a 2kW heater. But I'd guess contingencies have to be designed in.

3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?


Basically it needs to go in ;-)

Conduit de-rates the cable current carrying capacity a bit, but not
normally enough to have a significant impact on the design.

The fact that I'm asking these questions tends towards telling him to
get an electrician - I can see this being a bit of a nightmare.


It ought to be relatively straight forward. You will likely want to
terminate the incoming feed (probably a SWA cable) in an insulated box,
and the connect that to the CU. That way you can have a local TT
earthing system for the shed with and earth spike.

If you are lucky and the sparks has not wired the whole submain from a
RCD protected supply, then you can have a split load CU in the shed to
keep the lights on a separate RCD to the sockets.

But
answers will help me understand it all better, and give him something to
think about.


Indeed. It will be a case of having a closer look at the starting point
(like how power was taken from the house supply, what type and sixe of
cable was used, and what the earthing arrangements are for the house
supply.


--
Cheers,

John.

/================================================== ===============\
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\================================================= ================/
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On 02/01/2019 22:52, RJH wrote:

It's more the 'client' - he's quite impatient and has a habit of looking
for fault when it isn't necessarily there. A sort of irritatingly
enquiring mind looking for shortcuts.


Set ground rules. If he doesn't obey them just don't go for a few weeks
til he rings up. Then warn him. Be as awkward as he is. Don't give him
an inch. It's the only way. I'm speaking from 45 years' experience
installing for private customers.

Bill
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On 02/01/2019 22:36, RJH wrote:
On 02/01/2019 22:14, Tim Watts wrote:
On 02/01/2019 21:05, RJH wrote:

3) Routing the wiring. He's intending to use 20mm plastic tube
conduit, which for layout reasons has to go up, round, and down to
the sockets/lights/switches. It'd obviously be neater to route all
the cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?


Yes - there's the fill factor:

https://www.rm-electrical.com/wp-con...Technical1.pdf


Excellent, thanks.


That's purely on space. In essence, if it fits easily, it's OK.


Are you proposing to use singles?


As in a single run of cable? I need to draw it all out, but at the very
least there'll be the 13A socket and the lighting cable running through
the conduit, to keep things neat.

The lighting cable could in theory be quite skinny - 3A, for the 160W load?


No - as in single insulated cores - if you are running 100% in trunking
or conduit, it makes sense - more manageable.

You can buy that by the metre in some electrical wholesales (think TLC do).

If you run T+E in conduit/trunking with multiple circuits you need to
apply a grouping factor (a 1 multiplier to the current carrying
caapcity of the cable).

I am not sure of the calculation with singles for multiple circuits -
did look at my Regs but couldn't find a table for that case.

--
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Default Wiring for a Shed ancillary question

Hi, In the past in a shed I used to work on equipment with a live chassis by
having it on the other side of an isolating transformer and earthing the non
live side, if you get my drift. After all this is just what replacing an
auto transformer would do to mains gear of that age.
However I used to fly by the seat of my pants in those days, and so what
I'd want to do with my new shed when its built is also to protect that
circuit with more than a 5 amp fuse.

Now I'm probably well outside of the law here on this one but two problems
come to mind. First what sort of breaker and also of course you would need
any gear connected to have a plug on it that could not, accidentally be put
into a standard socket as that would be disaster on many levels. are there
special plugs or sockets for this kind of use?

Brian

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Note this Signature is meaningless.!
"Tim Watts" wrote in message
...
On 02/01/2019 21:05, RJH wrote:

3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the cables
in one run of conduit - is there some guidance relating to stuffing
conduit with cable?


Yes - there's the fill factor:

https://www.rm-electrical.com/wp-con...Technical1.pdf


That's purely on space. In essence, if it fits easily, it's OK.


Are you proposing to use singles?

--
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In message , RJH writes
A friend has build a fairly elaborate shed - about 5m x 5m, insulated.
An electrician has installed a 63A feed from the main supply, using a
consumer unit and an MCB, to the shed (which is 75m from the house),
terminated with a 13A socket, with lighting spurred off the socket.

He's asked me to help him install 6 double sockets and wiring/switching
to 4 x 4' 50W LED batten lights.

I'm not sure yet whether I'm going to do it - I'd do it for myself, but
he's quite impatient, and I don't think he'd be happy with the 3 months
I'd give myself to exercise excessive caution. Anyway, a couple of Qs:

1) Would you use a consumer unit in the shed? If so, what's the MCB and
RCD situation? I's assume the CU and MCB/RCD arrangements at the main
supply have some bearing on this.

2) Ring or radial for the sockets? I've had a look at the DIY wiki:
http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners
I think it's going to need a ring because he's factoring in an oven
(3kW, for pottery) at a later date. But it'd be a lot easier to do a
dedicated oven socket on a separate feed from however (1) is organised,
and a radial for the remaining 5 sockets. I don't follow where the
'20A' in the radial comes from in the wiki diagram - how is a radial
socket circuit designed for a particular use? The only anticipated high
current device is a 2kW heater. But I'd guess contingencies have to be
designed in.

3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?

The fact that I'm asking these questions tends towards telling him to
get an electrician - I can see this being a bit of a nightmare. But
answers will help me understand it all better, and give him something
to think about.


I'll leave others to comment on split load consumer units but the length
of supply run should push you to a local earth rod.

You mention layout reasons for going up and down with 20mm conduit. If
practical, it can be much simpler to use 50mm metal duct at the outlet
level.
I mount twin socket outlets directly above or below the duct using 20mm
metal conduit connectors and brass bushes.
The duct has ample space for using 4mm singles and allows easy access
for afterthoughts:-)
Best to trap the cables away from the cover (sharp edges). I use short
lengths of flexible plastic duct.


--
Tim Lamb


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Default Wiring for a Shed ancillary question

Brian Gaff wrote:

Hi, In the past in a shed I used to work on equipment with a live chassis by
having it on the other side of an isolating transformer and earthing the non
live side, if you get my drift. After all this is just what replacing an
auto transformer would do to mains gear of that age.
However I used to fly by the seat of my pants in those days, and so what
I'd want to do with my new shed when its built is also to protect that
circuit with more than a 5 amp fuse.

Now I'm probably well outside of the law here on this one but two problems
come to mind. First what sort of breaker and also of course you would need
any gear connected to have a plug on it that could not, accidentally be put
into a standard socket as that would be disaster on many levels. are there
special plugs or sockets for this kind of use?

Brian


I used to do the same, but I haven't seen any live chassis equipment I
wanted to repair for about fifty years. And getting the series heater
replacement valves might prove expensive.

Having said that, I can't think of any way an isolated supply with one
side connected to local earth could be protected in any way that doesn't
make it more hazardous to the operator rather than less.

--

Roger Hayter
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Default Wiring for a Shed

On 02/01/2019 21:05, RJH wrote:
A friend has build a fairly elaborate shed - about 5m x 5m, insulated.
An electrician has installed a 63A feed from the main supply, using a
consumer unit and an MCB, to the shed (which is 75m from the house),
terminated with a 13A socket, with lighting spurred off the socket.

He's asked me to help him install 6 double sockets and wiring/switching
to 4 x 4' 50W LED batten lights.

I'm not sure yet whether I'm going to do it - I'd do it for myself, but
he's quite impatient, and I don't think he'd be happy with the 3 months
I'd give myself to exercise excessive caution. Anyway, a couple of Qs:

1) Would you use a consumer unit in the shed? If so, what's the MCB and
RCD situation? I's assume the CU and MCB/RCD arrangements at the main
supply have some bearing on this.

2) Ring or radial for the sockets? I've had a look at the DIY wiki:
http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners
I think it's going to need a ring because he's factoring in an oven
(3kW, for pottery) at a later date. But it'd be a lot easier to do a
dedicated oven socket on a separate feed from however (1) is organised,
and a radial for the remaining 5 sockets. I don't follow where the '20A'
in the radial comes from in the wiki diagram - how is a radial socket
circuit designed for a particular use? The only anticipated high current
device is a 2kW heater. But I'd guess contingencies have to be designed in.

3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?

The fact that I'm asking these questions tends towards telling him to
get an electrician - I can see this being a bit of a nightmare. But
answers will help me understand it all better, and give him something to
think about.


It's a very detailed point but given it's a shed with an oven (and other
tools?) I'd provide 2 (at least) independent light sources so tripping
one MCB/RCD doesn't leave you in the dark. If the whole supply might be
cut off by a trip in the house then a non-maintained emergency light
could kill 2 birds with one pony*.


* 25 pounds that is - or guineas if he is a professional


--
Robin
reply-to address is (intended to be) valid
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On Thursday, 3 January 2019 11:22:40 UTC, Roger Hayter wrote:
Brian Gaff wrote:

Hi, In the past in a shed I used to work on equipment with a live chassis by
having it on the other side of an isolating transformer and earthing the non
live side, if you get my drift. After all this is just what replacing an
auto transformer would do to mains gear of that age.
However I used to fly by the seat of my pants in those days, and so what
I'd want to do with my new shed when its built is also to protect that
circuit with more than a 5 amp fuse.

Now I'm probably well outside of the law here on this one but two problems
come to mind. First what sort of breaker and also of course you would need
any gear connected to have a plug on it that could not, accidentally be put
into a standard socket as that would be disaster on many levels. are there
special plugs or sockets for this kind of use?

Brian


I used to do the same, but I haven't seen any live chassis equipment I
wanted to repair for about fifty years. And getting the series heater
replacement valves might prove expensive.


under an hour's pay each

Having said that, I can't think of any way an isolated supply with one
side connected to local earth could be protected in any way that doesn't
make it more hazardous to the operator rather than less.


RCD after the iso transformer.


NT
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On 03/01/2019 10:16, Tim Watts wrote:
On 02/01/2019 22:36, RJH wrote:
On 02/01/2019 22:14, Tim Watts wrote:
On 02/01/2019 21:05, RJH wrote:

3) Routing the wiring. He's intending to use 20mm plastic tube
conduit, which for layout reasons has to go up, round, and down to
the sockets/lights/switches. It'd obviously be neater to route all
the cables in one run of conduit - is there some guidance relating
to stuffing conduit with cable?

Yes - there's the fill factor:

https://www.rm-electrical.com/wp-con...Technical1.pdf


Excellent, thanks.


That's purely on space. In essence, if it fits easily, it's OK.


Are you proposing to use singles?


As in a single run of cable? I need to draw it all out, but at the
very least there'll be the 13A socket and the lighting cable running
through the conduit, to keep things neat.

The lighting cable could in theory be quite skinny - 3A, for the 160W
load?


No - as in single insulated cores - if you are running 100% in trunking
or conduit, it makes sense - more manageable.


I was going to say that too


You can buy that by the metre in some electrical wholesales (think TLC do).


Surely he's going to need a reel of each


If you run T+E in conduit/trunking with multiple circuits you need to
apply a grouping factor (a 1 multiplier to the current carrying
caapcity of the cable).

I am not sure of the calculation with singles for multiple circuits -
did look at my Regs but couldn't find a table for that case.


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In article ,
Brian Gaff wrote:
Hi, In the past in a shed I used to work on equipment with a live
chassis by having it on the other side of an isolating transformer and
earthing the non live side, if you get my drift.


If you earth one leg of an isolation transformer, you are back to how
mains is without one. Leaving the secondary floating means you have to
touch both legs to get a 'shock'

But these days, you'd use an RCD for safety purposes.

--
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Dave Plowman London SW
To e-mail, change noise into sound.


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On 03/01/2019 10:32, Tim Lamb wrote:


I'll leave others to comment on split load consumer units but the length
of supply run should push you to a local earth rod.


+1

And all RCBOs.



--
Adam
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wrote:

On Thursday, 3 January 2019 11:22:40 UTC, Roger Hayter wrote:
Brian Gaff wrote:

Hi, In the past in a shed I used to work on equipment with a live
chassis by having it on the other side of an isolating transformer and
earthing the non live side, if you get my drift. After all this is
just what replacing an auto transformer would do to mains gear of that
age. However I used to fly by the seat of my pants in those days, and
so what
I'd want to do with my new shed when its built is also to protect that
circuit with more than a 5 amp fuse.

Now I'm probably well outside of the law here on this one but two
problems come to mind. First what sort of breaker and also of course
you would need any gear connected to have a plug on it that could not,
accidentally be put into a standard socket as that would be disaster
on many levels. are there special plugs or sockets for this kind of
use?

Brian


I used to do the same, but I haven't seen any live chassis equipment I
wanted to repair for about fifty years. And getting the series heater
replacement valves might prove expensive.


under an hour's pay each


Fascinated to know you can still get them. Though I know some LOP
valves are still in use.



Having said that, I can't think of any way an isolated supply with one
side connected to local earth could be protected in any way that doesn't
make it more hazardous to the operator rather than less.


RCD after the iso transformer.


That only works if you reference the secondary voltage to earth before
the RCD. Otherwise there is nowhere for unbalanced leakage to go. And
I am not sure that is actually safer, as it does not protect against a
shock from live to chassis, the most dangerous kind.





NT



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Roger Hayter
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Default Wiring for a Shed ancillary question

On Thursday, 3 January 2019 21:21:18 UTC, Roger Hayter wrote:
tabbypurr wrote:
On Thursday, 3 January 2019 11:22:40 UTC, Roger Hayter wrote:
Brian Gaff wrote:

Hi, In the past in a shed I used to work on equipment with a live
chassis by having it on the other side of an isolating transformer and
earthing the non live side, if you get my drift. After all this is
just what replacing an auto transformer would do to mains gear of that
age. However I used to fly by the seat of my pants in those days, and
so what
I'd want to do with my new shed when its built is also to protect that
circuit with more than a 5 amp fuse.

Now I'm probably well outside of the law here on this one but two
problems come to mind. First what sort of breaker and also of course
you would need any gear connected to have a plug on it that could not,
accidentally be put into a standard socket as that would be disaster
on many levels. are there special plugs or sockets for this kind of
use?

Brian

I used to do the same, but I haven't seen any live chassis equipment I
wanted to repair for about fifty years. And getting the series heater
replacement valves might prove expensive.


under an hour's pay each


Fascinated to know you can still get them. Though I know some LOP
valves are still in use.


What can't you get on ebay?

Having said that, I can't think of any way an isolated supply with one
side connected to local earth could be protected in any way that doesn't
make it more hazardous to the operator rather than less.


RCD after the iso transformer.


That only works if you reference the secondary voltage to earth before
the RCD. Otherwise there is nowhere for unbalanced leakage to go. And
I am not sure that is actually safer, as it does not protect against a
shock from live to chassis, the most dangerous kind.


Isos make a shock require 2 touch points instead of one - an improvement in safety. But be a bit wary of isos, one can sometimes still get shocks from them. All is not as it first appears.


NT
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