I'm converting my garage to a small woodworking
workshop. I need to install a CU in the workshop
and run a cable from the house CU. As it happens
the house CU will be replaced at the same time.
I know how to do the cable calc, but I'm struggling
with two aspects. One is understanding what I use
for Ib (Design Current), the other is to do with
Type B / Type C MCBs.

Design current first.
-----------------------
This is design current of the workshop. I'm not
using diversity because I am very clear about
what the max current will be and that it will occur.
What I don't know, is what to do about motor
startup currents. Do I have to take them into
account for Ib? Some of the machines
(Eg.. 3Kw Hammer Sawtable) have soft start
so I imagine the startup currents are handled by
the electronics in the machine. Others, like the
2.2Kw Axminster ADE4000 Dust Extractor
don't have soft start. Axminster have told me
that I should double the running current and add
another 15% in cold weather.

MCBs
-------
My thinking is that I may need Type C MCBs in
the workshop CU. I am really gozzy on the
differences/benefits/requirements re Type B and
Type C. My only understanding (apart from the
various graphs/charts in the Regs) is that the Type C
is less sensitive to startup currents. How do I
determine if Type C MCBs are needed? Also, if I
have Type Cs in the workshop, does that mean that
I must have a Type C for this circuit in the house CU.
If so I think I might have to run a separate (larger)
CPC to satisfy the Shock Protection requirements.

Thoughts?

Oh - and BTW - I know about Part P - before we go
down that route!!! :-)

Many thanks,
Roy

RzB wrote:

Design current first.
-----------------------
This is design current of the workshop. I'm not
using diversity because I am very clear about
what the max current will be and that it will occur.
What I don't know, is what to do about motor
startup currents. Do I have to take them into
account for Ib? Some of the machines
(Eg.. 3Kw Hammer Sawtable) have soft start
so I imagine the startup currents are handled by
the electronics in the machine. Others, like the
2.2Kw Axminster ADE4000 Dust Extractor
don't have soft start. Axminster have told me
that I should double the running current and add
another 15% in cold weather.

Individual motor circuits for all but tiny motors I presume? Ib can be
taken to the motor's full-load running current (FLC) as given on the
rating plate. That's certainly OK for cable sizing. It's only when you
get to really big motors (10s of kW) that you need to worry about the
effect of starting current on cables. That said, don't skimp on cable
size, it's not a major cost and keeping the impedance down helps with
starting.

MCBs
-------
My thinking is that I may need Type C MCBs in
the workshop CU. I am really gozzy on the
differences/benefits/requirements re Type B and
Type C. My only understanding (apart from the
various graphs/charts in the Regs) is that the Type C
is less sensitive to startup currents.

Type B will trip "instantaneously" at between 3 and 5 times In (the
nominal current). For type C it's 5 to 10 times and for type D 10 to 20.

How do I determine if Type C MCBs are needed?

As a starting points use type C for all motor circuits and type B for
your lighting, 13 A sockets circuit and for any electric heating. If
you experience motor-start tripping you can either increase the MCB size
by one step, or go to type D, after checking that the cable is s/c fault
protected (adiabatic equation). This assumes overload protection is
provided by an electronic or thermal overload device in the motor
starter, which should be the case.

Also, if I have Type Cs in the workshop, does that mean that I must
have a Type C for this circuit in the house CU.

The best option at the house end, discrimination wise) is an HRC fuse
(cartridge fuse) in a separate switch-fuse unit. (Tee into the meter
tails using a service connector block.)

If so I think I might have to run a separate (larger) CPC to satisfy
the Shock Protection requirements.

Total design current? Cable type, size and length? Is house earthing
PME or TN-S?

Thoughts?

Wire your workshop in conduit and trunking so that it's easy to make
mods. Changes will be inevitable over time. A good strategy is a ring
of trunking (say 50 x 50 mm) round the walls at high level, with conduit
drops to sockets, switches and motor starters, and upward runs to lighting.

13 A sockets should be on an RCD protected circuit(s).

--
Andy

Andy,
many thanks for your help...

See inline comments..

Roy

"Andy Wade" wrote in message
...
RzB wrote:

Design current first.
-----------------------
This is design current of the workshop. I'm not
using diversity because I am very clear about
what the max current will be and that it will occur.
What I don't know, is what to do about motor
startup currents. Do I have to take them into
account for Ib? Some of the machines
(Eg.. 3Kw Hammer Sawtable) have soft start
so I imagine the startup currents are handled by
the electronics in the machine. Others, like the
2.2Kw Axminster ADE4000 Dust Extractor
don't have soft start. Axminster have told me
that I should double the running current and add
another 15% in cold weather.

Individual motor circuits for all but tiny motors I presume? Ib can be
taken to the motor's full-load running current (FLC) as given on the
rating plate. That's certainly OK for cable sizing. It's only when you
get to really big motors (10s of kW) that you need to worry about the
effect of starting current on cables. That said, don't skimp on cable
size, it's not a major cost and keeping the impedance down helps with
starting.

Yes - I won't skimp - I would like to keep the Vd to a
mimimum. What would you think is a good goal to aim for?


MCBs
-------
My thinking is that I may need Type C MCBs in
the workshop CU. I am really gozzy on the
differences/benefits/requirements re Type B and
Type C. My only understanding (apart from the
various graphs/charts in the Regs) is that the Type C
is less sensitive to startup currents.

Type B will trip "instantaneously" at between 3 and 5 times In (the
nominal current). For type C it's 5 to 10 times and for type D 10 to 20.

How do I determine if Type C MCBs are needed?

As a starting points use type C for all motor circuits and type B for your
lighting, 13 A sockets circuit and for any electric heating. If you
experience motor-start tripping you can either increase the MCB size by
one step, or go to type D, after checking that the cable is s/c fault
protected (adiabatic equation). This assumes overload protection is
provided by an electronic or thermal overload device in the motor starter,
which should be the case.

Yes - I hink so... not sure about the Dust Extractor but I
will check with Axminster.


Also, if I have Type Cs in the workshop, does that mean that I must
have a Type C for this circuit in the house CU.

The best option at the house end, discrimination wise) is an HRC fuse
(cartridge fuse) in a separate switch-fuse unit. (Tee into the meter
tails using a service connector block.)

Hmmm - Lost me here... Are you saying that I shouldn't be
taking the workshop circuit through the house CU?
Why wouldn't this just be one of the circuits off an MCB
on the house CU?


If so I think I might have to run a separate (larger) CPC to satisfy
the Shock Protection requirements.

Total design current? Cable type, size and length? Is house earthing PME
or TN-S?

OK - I have a 6mm cable already in place and I intend
to leave that there to drive the workshop lighting and
the external approach lighting. Was thinking of having
a separate CU in the garage for this...

Design current - ignoring startup currents - see...

http://www.gillandroy.com/diy/workshop/electrics

Workshop is attached to house... and distance between
house CU and workshop CU is about 25M.

House is PME. Cable running through loft so might get
to 40degC ambient in the summer - yes/no? Also cavity
wall insulation will enclose cable when passing through
wall fo a couple of inches... No grouping.. Otherwise -
cable just clipped to wall/rafters?

After calcs, I was considering using 16mm T & E from
house to Workshop. But I'm not sure what CPC size comes
with standard 16mm T&E?

Runs from workshop CU to machines are all less than 5M.


Thoughts?

Wire your workshop in conduit and trunking so that it's easy to make mods.
Changes will be inevitable over time. A good strategy is a ring of
trunking (say 50 x 50 mm) round the walls at high level, with conduit
drops to sockets, switches and motor starters, and upward runs to
lighting.

13 A sockets should be on an RCD protected circuit(s).

Yes - that is what I was thinking - except that I'll probably
run the lighting circuits in the roofspace.


--
Andy

"RzB" wrote in message
...
Andy,
many thanks for your help...

See inline comments..

Roy

"Andy Wade" wrote in message
...
RzB wrote:

Design current first.
-----------------------
This is design current of the workshop. I'm not
using diversity because I am very clear about
what the max current will be and that it will occur.
What I don't know, is what to do about motor
startup currents. Do I have to take them into
account for Ib? Some of the machines
(Eg.. 3Kw Hammer Sawtable) have soft start
so I imagine the startup currents are handled by
the electronics in the machine. Others, like the
2.2Kw Axminster ADE4000 Dust Extractor
don't have soft start. Axminster have told me
that I should double the running current and add
another 15% in cold weather.

Individual motor circuits for all but tiny motors I presume? Ib can be
taken to the motor's full-load running current (FLC) as given on the
rating plate. That's certainly OK for cable sizing. It's only when you
get to really big motors (10s of kW) that you need to worry about the
effect of starting current on cables. That said, don't skimp on cable
size, it's not a major cost and keeping the impedance down helps with
starting.

Yes - I won't skimp - I would like to keep the Vd to a
mimimum. What would you think is a good goal to aim for?


MCBs
-------
My thinking is that I may need Type C MCBs in
the workshop CU. I am really gozzy on the
differences/benefits/requirements re Type B and
Type C. My only understanding (apart from the
various graphs/charts in the Regs) is that the Type C
is less sensitive to startup currents.

Type B will trip "instantaneously" at between 3 and 5 times In (the
nominal current). For type C it's 5 to 10 times and for type D 10 to 20.

How do I determine if Type C MCBs are needed?

As a starting points use type C for all motor circuits and type B for
your lighting, 13 A sockets circuit and for any electric heating. If you
experience motor-start tripping you can either increase the MCB size by
one step, or go to type D, after checking that the cable is s/c fault
protected (adiabatic equation). This assumes overload protection is
provided by an electronic or thermal overload device in the motor
starter, which should be the case.

Yes - I hink so... not sure about the Dust Extractor but I
will check with Axminster.


Also, if I have Type Cs in the workshop, does that mean that I must
have a Type C for this circuit in the house CU.

The best option at the house end, discrimination wise) is an HRC fuse
(cartridge fuse) in a separate switch-fuse unit. (Tee into the meter
tails using a service connector block.)

Hmmm - Lost me here... Are you saying that I shouldn't be
taking the workshop circuit through the house CU?
Why wouldn't this just be one of the circuits off an MCB
on the house CU?


If so I think I might have to run a separate (larger) CPC to satisfy
the Shock Protection requirements.

Total design current? Cable type, size and length? Is house earthing
PME or TN-S?

OK - I have a 6mm cable already in place and I intend
to leave that there to drive the workshop lighting and
the external approach lighting. Was thinking of having
a separate CU in the garage for this...

Design current - ignoring startup currents - see...

http://www.gillandroy.com/diy/workshop/electrics

Workshop is attached to house... and distance between
house CU and workshop CU is about 25M.

House is PME. Cable running through loft so might get
to 40degC ambient in the summer - yes/no? Also cavity
wall insulation will enclose cable when passing through
wall fo a couple of inches... No grouping.. Otherwise -
cable just clipped to wall/rafters?

After calcs, I was considering using 16mm T & E from
house to Workshop. But I'm not sure what CPC size comes
with standard 16mm T&E?

Runs from workshop CU to machines are all less than 5M.


Thoughts?

Wire your workshop in conduit and trunking so that it's easy to make
mods. Changes will be inevitable over time. A good strategy is a ring of
trunking (say 50 x 50 mm) round the walls at high level, with conduit
drops to sockets, switches and motor starters, and upward runs to
lighting.

13 A sockets should be on an RCD protected circuit(s).

Yes - that is what I was thinking - except that I'll probably
run the lighting circuits in the roofspace.


--
Andy


One point of course is that I won't be running 4kW of heaters
when the roof space is at 40degC!!!! :-)

Roy

RzB wrote:

"RzB" wrote in message
...

Yes - I won't skimp - I would like to keep the Vd to a
mimimum. What would you think is a good goal to aim for?

The old 2.5% limit is a good guide.

The best option at the house end, discrimination wise) is an HRC fuse
(cartridge fuse) in a separate switch-fuse unit. (Tee into the meter
tails using a service connector block.)

Hmmm - Lost me here... Are you saying that I shouldn't be
taking the workshop circuit through the house CU?
Why wouldn't this just be one of the circuits off an MCB
on the house CU?

It's better not to, especially as you're really looking at a 50 or 60/63
amp distribution circuit for the workshop. The problem with cascading
MCBs can be lack of discrimination on s/c faults - both MCBs may trip.
(This may not matter to you though, as you've got a separate feed for
lighting.) You also need to consider whether the house CU and indeed
the supply is OK for ~45 A of extra load. (Any electric showers or
space heating in the house?)

Design current - ignoring startup currents - see...
http://www.gillandroy.com/diy/workshop/electrics

Workshop is attached to house... and distance between
house CU and workshop CU is about 25M.

House is PME. Cable running through loft so might get
to 40degC ambient in the summer - yes/no? Also cavity
wall insulation will enclose cable when passing through
wall fo a couple of inches... No grouping.. Otherwise -
cable just clipped to wall/rafters?

After calcs, I was considering using 16mm T & E from
house to Workshop. But I'm not sure what CPC size comes
with standard 16mm T&E?

CPC is 6 mm^2. Yes, 16 mm^2 for the cable sounds about right, it'll
give you plenty of current rating in hand and keeps the voltage drop
down to 2%. A separate parallel 10 or 16 mm^2 CPC would be prudent,
although I haven't done the calculations to see whether it is strictly
necessary - this depends on your choice of overcurrent device at the
house end in any case.

--
Andy

Others, like the 2.2Kw Axminster ADE4000 Dust Extractor
don't have soft start. Axminster have told me that I
should double the running current and add another 15%
in cold weather.

Your design current doesn't include startup currents. You want to use Type B
if at all possible, as they are safer. These can accept a startup current up
to 3 times the design current, which would appear to be fine, as your worst
case scenario is the 2.2kW at x2.3 current which will give 22A which is not
going to trouble the wiring or a 32A Type B MCB, even if the ring is already
nominally fully loaded, unless the startup current lasts for an unduly long
period of time.

Christian.

"Andy Wade" wrote in message
...
RzB wrote:

"RzB" wrote in message
...

---- snip

It's better not to, especially as you're really looking at a 50 or 60/63
amp distribution circuit for the workshop. The problem with cascading
MCBs can be lack of discrimination on s/c faults - both MCBs may trip.
(This may not matter to you though, as you've got a separate feed for
lighting.) You also need to consider whether the house CU and indeed the
supply is OK for ~45 A of extra load. (Any electric showers or space
heating in the house?)

Ahh,... Now I just hadn't even thought about the
total current coming in to the house. That would
have popped up when I looked at diversity for the
house as part on the new CU work. Hmmm... What
happens if the calcs come out over 100A? Do I just
ask the suppliers for "more please" ! Hmm... We have
a shower - only used very occasionally by visitors so
probably not a big deal. But it will probably blow the
diversity calcs. Hmm...

------- snip

CPC is 6 mm^2. Yes, 16 mm^2 for the cable sounds about right, it'll give
you plenty of current rating in hand and keeps the voltage drop down to
2%. A separate parallel 10 or 16 mm^2 CPC would be prudent, although I
haven't done the calculations to see whether it is strictly necessary -
this depends on your choice of overcurrent device at the house end in any
case.


Yes - I need to redo the calcs but I believe the 6mm
CPC will be OK if I have a Type B in the house.
I think I would still run a separate CPC though.
However I can see that your suggestion of a fuse
is preferable. I need to redo the calcs for this. I
would imagine 6mm would not be enough for this.

Many thanks,
Roy

"Christian McArdle" wrote in message
...
Others, like the 2.2Kw Axminster ADE4000 Dust Extractor
don't have soft start. Axminster have told me that I
should double the running current and add another 15%
in cold weather.

Your design current doesn't include startup currents. You want to use Type
B
if at all possible, as they are safer. These can accept a startup current
up
to 3 times the design current, which would appear to be fine, as your
worst
case scenario is the 2.2kW at x2.3 current which will give 22A which is
not
going to trouble the wiring or a 32A Type B MCB, even if the ring is
already
nominally fully loaded, unless the startup current lasts for an unduly
long
period of time.

Christian.

Christian,

I was expecting to provide separate circuits to each
of the static machines in the workshop. So there
won't be any ring to worry about. The workshop
sockets ring will be protected by an RCBO.

Many thanks for your help,
Roy

I was expecting to provide separate circuits to each
of the static machines in the workshop. So there
won't be any ring to worry about. The workshop
sockets ring will be protected by an RCBO.

I would say that a fixed 2.2kW motor appliance with total inrush current of
22A will be fine on a 16A Type B MCB, which won't instantaneous trip until
at least 48A. Obviously if it takes an age to spin up then it could blow the
thermal curve, although at only 6A over the 16A rating, this is unlikely.

Christian.

Andy,

I have re-thought the workshop loading and done
some cable calcs and put them on...

http://www.gillandroy.com/diy/workshop/electrics

It looks like a 16mm T&E with 6mm CPC will
satisfy the regs with whatever protection is back at
the house. However, I think I will put in a separate
10mm CPC (belt & braces) and have a fused
switched by the house CU as you suggested.

I'm not clear about the sort of Fuse to use ?
BS 88, BS1361 ? Or what? Or will that get
determined by the switch-fuse unit.

Do I take it this is the sort of thing you are suggesting...

http://www.tlc-direct.co.uk/Products/WY108.html

Many thanks for your help,
Roy

RzB wrote:

Andy,
I have re-thought the workshop loading and done
some cable calcs and put them on...
http://www.gillandroy.com/diy/workshop/electrics

That URL gives me a blank page (in Firefox) and the only source I can
see (with whitespace removed) is:

!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
ptable cellpadding=10 cellspacing=0 border=0tr/p

It looks like a 16mm T&E with 6mm CPC will
satisfy the regs with whatever protection is back at
the house. However, I think I will put in a separate
10mm CPC (belt & braces) and have a fused
switched by the house CU as you suggested.

I'm not clear about the sort of Fuse to use ?
BS 88, BS1361 ? Or what? Or will that get
determined by the switch-fuse unit.

Either, and yes (obviously) it will be determined by the type of fuse
carrier in the switch-fuse.

Do I take it this is the sort of thing you are suggesting...
http://www.tlc-direct.co.uk/Products/WY108.html

That's *exactly* what I had in mind. My own workshop installation is
fed through a 108M (the metalclad version) fitted with a 45 A fuse. You
could also look at things like the MEM Excel range, which take BS 88
fuses, but they're much more expensive for no real advantage.

--
Andy

"Andy Wade" wrote in message
...
RzB wrote:

Andy,
I have re-thought the workshop loading and done
some cable calcs and put them on...
http://www.gillandroy.com/diy/workshop/electrics

That URL gives me a blank page (in Firefox) and the only source I can see
(with whitespace removed) is:


Yes - Servers got moved today... sorry

Should be OK now..

Many thanks,
Roy

"RzB" wrote in message
...

"Andy Wade" wrote in message
...
RzB wrote:

Andy,
I have re-thought the workshop loading and done
some cable calcs and put them on...
http://www.gillandroy.com/diy/workshop/electrics

That URL gives me a blank page (in Firefox) and the only source I can see
(with whitespace removed) is:


Yes - Servers got moved today... sorry

Should be OK now..

Many thanks,
Roy

Hmm... now seems broken again! D'oh...

"RzB" wrote in message
...

"RzB" wrote in message
...

"Andy Wade" wrote in message
...
RzB wrote:

Andy,
I have re-thought the workshop loading and done
some cable calcs and put them on...
http://www.gillandroy.com/diy/workshop/electrics

That URL gives me a blank page (in Firefox) and the only source I can
see (with whitespace removed) is:


Yes - Servers got moved today... sorry

Should be OK now..

Many thanks,
Roy

Hmm... now seems broken again! D'oh...


OK - Should be OK now.... !!!

RzB wrote:

OK - Should be OK now.... !!!

Yep. My comments on your calcs a

1. Current rating: You've used It = Ib/(Ca*Ci). Since overload
protection is required here this should be In/(Ca*Ci) - i.e. based on
the device rating, not the design current. Moreover in your case the Ca
factor (for loft temperature) and Ci factor don't apply simultaneously
(the cable thro' the wall won't be at 40 deg. and the cable in the loft
will be well-supported away from thermal insulation). With Ib = 41.3 A
and your intention of using the Wylex 108, we can select the 45 A BS
1361 fuse, hence It = 45 A / 0.81 = 56 A (10 mm^2 still OK). Or with a
60 A fuse we get It = 74 A (16 mm^2 required).

2. Shock protection: your calcs will be on the conservative side because
you've assumed 70 deg. conductor temperature (the 1.2 factor). In fact
the greatest part of the cable's length will be running well under its
rated current, so the loop resistance to be added to Ze is
correspondingly less.

3. CPC thermal compliance and disconnection time, with 6 mm^2 CPC and 50
A Type C MCB: fault current at 479 A[*] is less than 10*In, therefore 5
seconds disconnection time is not necessarily achieved. Design is
non-compliant, go no further (or retry with larger CPC). For the Type B
yes, it's OK to use 0.1 s (compliant), ideally use manufacturer's
published I^2*t data, which can be more favourable.
[*] The fault current will fall as the cable heats up, so you have to
err on the pessimistic side here when anything is marginal. Design
based on the use of measured values of Ze is discouraged, since this
value is outside your control. In principle the DNO could alter their
network, resulting in a higher value.

Incidentally, are there any metal service pipes or other
extraneous-conductive-parts entering the workshop? If so, you may need
local bonding to the earth bar in your dis-board - see Regulation
413-02-13 (a challenging read).

--
Andy

Andy,

Apols for delay - have been away for the weekend...

See inline comments..

Many thanks for your VERY helpful feedback...

I think I will be going with 16mm T&E + additional
CPC - 10mm ? Through a separate 45A or perhaps 60A
Fused switch.

BTW - If, after doing the house diversity calcs, it comes
out greater than 100A, what is the likly response
from the supplier?

Many thanks,
Roy

"Andy Wade" wrote in message
...
RzB wrote:

OK - Should be OK now.... !!!

Yep. My comments on your calcs a

1. Current rating: You've used It = Ib/(Ca*Ci). Since overload
protection is required here this should be In/(Ca*Ci) - i.e. based on the
device rating, not the design current.

Yes - daft typo... formula sasy In then I use Ib... D'oh...

Moreover in your case the Ca factor (for loft temperature) and Ci factor
don't apply simultaneously (the cable thro' the wall won't be at 40 deg.
and the cable in the loft will be well-supported away from thermal
insulation).

My understanding was to use both - really don't understand the
rationalle behind this. However I think the calcs come out OK
with 16mm^2 whatever factors are used!

With Ib = 41.3 A and your intention of using the Wylex 108, we can select
the 45 A BS 1361 fuse, hence It = 45 A / 0.81 = 56 A (10 mm^2 still OK).
Or with a 60 A fuse we get It = 74 A (16 mm^2 required).

Yes - OK.

2. Shock protection: your calcs will be on the conservative side because
you've assumed 70 deg. conductor temperature (the 1.2 factor). In fact
the greatest part of the cable's length will be running well under its
rated current, so the loop resistance to be added to Ze is correspondingly
less.

Yes - understand...


3. CPC thermal compliance and disconnection time, with 6 mm^2 CPC and 50 A
Type C MCB: fault current at 479 A[*] is less than 10*In, therefore 5
seconds disconnection time is not necessarily achieved. Design is
non-compliant, go no further (or retry with larger CPC).

Yes - no need to do adiabatic calc if the 5sec time is not met on
the time const graph table.

For the Type B yes, it's OK to use 0.1 s (compliant), ideally use
manufacturer's published I^2*t data, which can be more favourable.


Yes - I understand.

[*] The fault current will fall as the cable heats up, so you have to err
on the pessimistic side here when anything is marginal.

Yes - I understand.

Design based on the use of measured values of Ze is discouraged, since
this value is outside your control. In principle the DNO could alter
their network, resulting in a higher value.

Yes - good point...


Incidentally, are there any metal service pipes or other
extraneous-conductive-parts entering the workshop? If so, you may need
local bonding to the earth bar in your dis-board - see Regulation
413-02-13 (a challenging read).

Not at the moment but there will be. Thanks for the reminder
re bonding.


--
Andy

RzB wrote:

BTW - If, after doing the house diversity calcs, it comes
out greater than 100A, what is the likly response
from the supplier?

I wouldn't worry too much, and I doubt that they will. From all you've
said I'd expect any overloads to be of fairly short duration (i.e.
minutes not hours) and not likely to do any great harm. (I'm assuming
here that you do have a 100 A main fuse, not a 60 or 80 A one.) Make
sure that nothing around the service position is getting excessively hot
- fishy smells are sure sign of problems.

--
Andy

"Andy Wade" wrote in message
...
RzB wrote:

BTW - If, after doing the house diversity calcs, it comes
out greater than 100A, what is the likly response
from the supplier?

I wouldn't worry too much, and I doubt that they will. From all you've
said I'd expect any overloads to be of fairly short duration (i.e. minutes
not hours) and not likely to do any great harm. (I'm assuming here that
you do have a 100 A main fuse, not a 60 or 80 A one.) Make sure that
nothing around the service position is getting excessively hot - fishy
smells are sure sign of problems.

--
Andy

Andy,

OK - Yes 100A.

Many, many thanks for your excellent help.

Roy