My home's electricity supply is overhead. Consequently (I think) our main
consumer board is fitted with an RCD. Presumably this means that there is
really no real need to use an RCD when using say a hedge trimmer or dirty
water pump, as the main RCD is going to trip and give the necessary
protection anyway in the case of any fault developing. Am I right in making
that assumption?

TIA

Keith

"Keith Dunbar" wrote in message
...
My home's electricity supply is overhead. Consequently (I think) our main
consumer board is fitted with an RCD. Presumably this means that there is
really no real need to use an RCD when using say a hedge trimmer or dirty
water pump, as the main RCD is going to trip and give the necessary
protection anyway in the case of any fault developing. Am I right in
making that assumption?

Leaving aside your first assumption which I don't think is true (but someone
will say), a whole house RCD may well be 100mA. Individual use circuits that
you describe should be protected by a 30mA RCD (more sensitive to faults by
a factor of 3), in that case one should still be used.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

In an earlier contribution to this discussion,
Keith Dunbar wrote:

My home's electricity supply is overhead. Consequently (I think) our
main consumer board is fitted with an RCD. Presumably this means
that there is really no real need to use an RCD when using say a
hedge trimmer or dirty water pump, as the main RCD is going to trip
and give the necessary protection anyway in the case of any fault
developing. Am I right in making that assumption?

TIA

Keith

No. It depends to some extent on when the house was built and/or electricity
supply installed. Overhead mains were used *long* before RCDs were
invented - and I suspect that lots of houses still have overhead supplies
without RCDs.

Even if you do have an RCD, a whole house unit may well have a higher
threshold current needed to trip it than one intended for use with garden
tools etc.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Keith Dunbar wrote:
My home's electricity supply is overhead. Consequently (I think) our main
consumer board is fitted with an RCD. Presumably this means that there is
really no real need to use an RCD when using say a hedge trimmer or dirty
water pump, as the main RCD is going to trip and give the necessary
protection anyway in the case of any fault developing. Am I right in making
that assumption?

TIA

Keith


If its 30mA you are street legal.However many including myself find that
this gives a lot of nusiance tripping,and I ahve uorated to 100mA on teh
whole board, which dies trip if something really is wrong, but not
otherwise. That means I really OUGHT to get around to putting 30mA trips
on the circuits that feed outside...

On Feb 25, 10:16*am, "Keith Dunbar" wrote:
My home's electricity supply is overhead. *Consequently (I think) our main
consumer board is fitted with an RCD. *

Does it have a test button? Is there a 'mA/milliamp' rating printed on
it?

cheers,
Pete.

"Pete C" wrote in message
...
On Feb 25, 10:16 am, "Keith Dunbar" wrote:
My home's electricity supply is overhead. Consequently (I think) our main
consumer board is fitted with an RCD.

Does it have a test button? Is there a 'mA/milliamp' rating printed on it?

There are 2 RCDs, one for the main house (probably rewired 40 years ago) and
one for the annexe (built about 15 years ago).

The RCD for the main house is only marked:
500V and 60A - made by Crabtree.
I can see no mention of its rating. Interestingly, it has two earth wires
wired into at the output end.

The RCD for the annexe is marked:
240V and 63A.
It is also marked with BS 4293 and n0.03A (is this a 30mA rating?)

Keith

Keith Dunbar wrote:
"Pete C" wrote in message
..
On Feb 25, 10:16 am, "Keith Dunbar" wrote:

My home's electricity supply is overhead. Consequently (I think) our main
consumer board is fitted with an RCD.

Does it have a test button? Is there a 'mA/milliamp' rating printed on it?

There are 2 RCDs, one for the main house (probably rewired 40 years ago) and
one for the annexe (built about 15 years ago).

The RCD for the main house is only marked:
500V and 60A - made by Crabtree.
I can see no mention of its rating. Interestingly, it has two earth wires
wired into at the output end.

Thats an ELCB, not an RCD. Which means you would gain a
safety benefit by using an RCD on outdoor tools.


NT

Huge wrote:

W-e-e-e-e-e-e-e-lll.

the 100/30 mA trip issue has already been raised.

Are you happy for the whole house to lose power because of your hedge trimmer?
We have an overhead/PME supply with a master RCD and I still use 30mA RCDs for
external supplies.

Worth noting that cascaded RCDs don't usually discriminate - so in the
event of a fault one or both will trip - and it is as likely that the
upstream one will go before the downstream one. The solution is a
upstream RCD with a time delay.

--
Cheers,

John.

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Keith Dunbar wrote:

There are 2 RCDs, one for the main house (probably rewired 40 years ago) and
one for the annexe (built about 15 years ago).

The RCD for the main house is only marked:
500V and 60A - made by Crabtree.
I can see no mention of its rating. Interestingly, it has two earth wires
wired into at the output end.

Does it look like:

http://wiki.diyfaq.org.uk/index.php?title=RCD#ELCB

If so then it is not a RCD and can not be relied upon to give adequate
protection from shock via direct contact with exposed wires etc.

The RCD for the annexe is marked:
240V and 63A.
It is also marked with BS 4293 and n0.03A (is this a 30mA rating?)

Yes, this is a modern RCD with a 30mA rating.

The main wiki article on RCDs might be worth a read for some background
on the implications of your current setup.

http://wiki.diyfaq.org.uk/index.php?title=RCD




--
Cheers,

John.

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wrote in message
...
Keith Dunbar wrote:
"Pete C" wrote in message
..
On Feb 25, 10:16 am, "Keith Dunbar" wrote:

My home's electricity supply is overhead. Consequently (I think) our
main
consumer board is fitted with an RCD.

Does it have a test button? Is there a 'mA/milliamp' rating printed on
it?

There are 2 RCDs, one for the main house (probably rewired 40 years ago)
and
one for the annexe (built about 15 years ago).

The RCD for the main house is only marked:
500V and 60A - made by Crabtree.
I can see no mention of its rating. Interestingly, it has two earth
wires
wired into at the output end.

Thats an ELCB, not an RCD. Which means you would gain a
safety benefit by using an RCD on outdoor tools.


NT

ELCB's are condemned now, since they can be rendered inoperable by parallel
earth paths. They should be replaced with an RCD unit.

"John Rumm" wrote in message
...
Keith Dunbar wrote:

There are 2 RCDs, one for the main house (probably rewired 40 years ago)
and one for the annexe (built about 15 years ago).

The RCD for the main house is only marked:
500V and 60A - made by Crabtree.
I can see no mention of its rating. Interestingly, it has two earth
wires wired into at the output end.

Does it look like:

http://wiki.diyfaq.org.uk/index.php?title=RCD#ELCB

If so then it is not a RCD and can not be relied upon to give adequate
protection from shock via direct contact with exposed wires etc.

The RCD for the annexe is marked:
240V and 63A.
It is also marked with BS 4293 and n0.03A (is this a 30mA rating?)

Yes, this is a modern RCD with a 30mA rating.

The main wiki article on RCDs might be worth a read for some background on
the implications of your current setup.

http://wiki.diyfaq.org.uk/index.php?title=RCD


Yes indeed, the "RCD" for the main house is in fact an ELCB identical to the
one in the photo at:

http://wiki.diyfaq.org.uk/index.php?title=RCD#ELCB

I appreciate the advice to have it replaced by an RCD. Am I right in
assuming that this cannot be done however without bringing the rest of the
40-year-old installation up to the latest modern standards, at what I guess
would be huge expense for a 1650s 4 bedroom, 3 reception room house?

Keith

In article ,
"John McLean" writes:

ELCB's are condemned now, since they can be rendered inoperable by parallel
earth paths.

Err, you misunderstand what they do. They are
designed to work with parallel earth paths.
If you have enough, they cease operating because
you have a good enough earth not to need them.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article ,
"Keith Dunbar" writes:
Yes indeed, the "RCD" for the main house is in fact an ELCB identical to the
one in the photo at:

http://wiki.diyfaq.org.uk/index.php?title=RCD#ELCB

I appreciate the advice to have it replaced by an RCD. Am I right in
assuming that this cannot be done however without bringing the rest of the
40-year-old installation up to the latest modern standards, at what I guess
would be huge expense for a 1650s 4 bedroom, 3 reception room house?

Not in my view, although some electricians might not do it.

A 40 year old installation, unless it's been badly hacked about,
shouldn't be in a dangerous condition, even though not to today's
standards. Even if you want to bring it up to todays standards,
you can probably retain most of the existing cabling.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Keith Dunbar wrote:

Yes indeed, the "RCD" for the main house is in fact an ELCB identical to the
one in the photo at:

http://wiki.diyfaq.org.uk/index.php?title=RCD#ELCB

I appreciate the advice to have it replaced by an RCD. Am I right in
assuming that this cannot be done however without bringing the rest of the
40-year-old installation up to the latest modern standards, at what I guess
would be huge expense for a 1650s 4 bedroom, 3 reception room house?

There is nothing stopping you updating part of the installation. The
only thing that really ought to be brought up to modern spec if not
present, is the main equipotential bonds with the water and other
service pipes.

You have a few options for upgrading, it depends a bit on what you want
to achieve and how far you want to go.

The simplest option is to go for the "whole house" RCD sat in a separate
enclosure, and basically replacing the ELCB that you have now. This is a
deprecated way of doing things, since it gives no discrimination between
faults - i.e. you lose all power on any trip. However it would add
greatly to to shock protection and would cost under £40 for the bits.

A much better but relatively simple solution would be to replace the
ELCB with a time delayed 100mA RCD, and then split the tails to add a
second CU after the new RCD. This CU could have a standard 30mA RCD on
its incomer. You would then move any power socket circuits to the new
CU. Total cost would probably be under £130 in parts and would offer
greatly enhanced protection.

--
Cheers,

John.

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Andrew Gabriel wrote:
In article ,
"John McLean" writes:

ELCB's are condemned now, since they can be rendered inoperable by parallel
earth paths.

Err, you misunderstand what they do. They are
designed to work with parallel earth paths.
If you have enough, they cease operating because
you have a good enough earth not to need them.

Exactly - a common misunderstanding. Plenty of ELCBs are still
in use and doing their job fine. What they do doesnt provide as
many safety benfits of RCDs, but they do do the job theyre needed
for effectively.


NT

John Rumm wrote:
Keith Dunbar wrote:

Yes indeed, the "RCD" for the main house is in fact an ELCB identical to the
one in the photo at:

http://wiki.diyfaq.org.uk/index.php?title=RCD#ELCB

I appreciate the advice to have it replaced by an RCD. Am I right in
assuming that this cannot be done however without bringing the rest of the
40-year-old installation up to the latest modern standards, at what I guess
would be huge expense for a 1650s 4 bedroom, 3 reception room house?

There is nothing stopping you updating part of the installation.

the only 'but' to that its not uncommon for old installs to not wont
work with an RCD due to minor issues that need to be hunted
down and fixed. So if you go for an RCD, budget for further work.

However its just one more example of solving a problem that isnt
worthwhile. The number of electrocution deaths per year is very
small, and if youre going to spend £50 and a day's work there are
far bigger risks you could solve with that.


NT

wrote:
Andrew Gabriel wrote:
In article ,
"John McLean" writes:

ELCB's are condemned now, since they can be rendered inoperable by parallel
earth paths.
Err, you misunderstand what they do. They are
designed to work with parallel earth paths.
If you have enough, they cease operating because
you have a good enough earth not to need them.

Exactly - a common misunderstanding. Plenty of ELCBs are still
in use and doing their job fine. What they do doesnt provide as
many safety benfits of RCDs, but they do do the job theyre needed
for effectively.

This does presume they are installed in the way intended. Most I have
seen are not alas...

It is also important to note they offer no protection from direct
contact shocks.

--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

wrote:

I appreciate the advice to have it replaced by an RCD. Am I right in
assuming that this cannot be done however without bringing the rest of the
40-year-old installation up to the latest modern standards, at what I guess
would be huge expense for a 1650s 4 bedroom, 3 reception room house?
There is nothing stopping you updating part of the installation.

the only 'but' to that its not uncommon for old installs to not wont
work with an RCD due to minor issues that need to be hunted
down and fixed. So if you go for an RCD, budget for further work.

That is another attraction of adding a separate CU so that you can
select individual circuits to protect. It leave the option open to move
one back to the old CU if required while hunting faults.

If the old install is tripping a 100mA RCD with leakage then it really
ought to be fixed as a matter of some urgency anyway since it indicates
that there is probably a serious insulation break down failure somewhere.

However its just one more example of solving a problem that isnt
worthwhile.

I don't agree with that as a general statement... you need to take into
account the likely users of the installation, and the uses it will be
put to.

The number of electrocution deaths per year is very
small, and if youre going to spend £50 and a day's work there are
far bigger risks you could solve with that.

Just because a shock does not actually kill you it does not mean that
you escape unscathed. The RCD protected installation will in many cases
reduce the severity of a range of injuries that can be caused by
electric shock including burns, arc flash injury, and muscular spasm
injury (and secondary injuries resulting from said spasms). Not to
mention the pain and distress that shocks can cause.

The number of serious shocks resulting from (mis) using *appliances* is
actually quite large - and it is here that 30mA (or lower) threshold RCD
protection will make a big impact on prognosis for recovery from the shock.


--
Cheers,

John.

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John Rumm wrote:
wrote:

The number of electrocution deaths per year is very
small, and if youre going to spend �50 and a day's work there are
far bigger risks you could solve with that.

Just because a shock does not actually kill you it does not mean that
you escape unscathed.

Certainly, and this applies to the other causes of death & injury
too.
Death numbers are the one thing we can quantify and compare, so
those are normally what are used for comparison.

If you look at the top killers, electrocution kills orders of
magnitude
fewer people than a goodly list of other things. I still say spending
your pocket money changing an ELCB to an RCD will give little
safety return compared to addressing other normal household
issues.

A smoke alarm in every room would give way more benefit - look at
the govt figures, 70,000 domestic fires a year, 400 annual deaths,
and smoke alarms only picking up a percentage of these for
various reasons. From Fire Statistics United Kingdom, 2001,
ODPM:

"A smoke alarm was absent in the fire area in 59% of dwelling fires
in 2001. These fires accounted for around 280 deaths and a further
7,300 non-fatal casualties."

Smoke alarms "failed to operate altogether in 8,100 cases (12%)"



However its just one more example of solving a problem that isnt
worthwhile.

I don't agree with that as a general statement... you need to take into
account the likely users of the installation, and the uses it will be
put to.

There might be exceptions for unusual uses, but for most of us I
dont think thats the prime issue


NT

In article ,
John Rumm writes:
wrote:
Andrew Gabriel wrote:
In article ,
"John McLean" writes:

ELCB's are condemned now, since they can be rendered inoperable by parallel
earth paths.
Err, you misunderstand what they do. They are
designed to work with parallel earth paths.
If you have enough, they cease operating because
you have a good enough earth not to need them.

Exactly - a common misunderstanding. Plenty of ELCBs are still
in use and doing their job fine. What they do doesnt provide as
many safety benfits of RCDs, but they do do the job theyre needed
for effectively.

This does presume they are installed in the way intended. Most I have
seen are not alas...

I can't think that I've ever seen one installed incorrectly.
I think there was a higher skill level amongst the electricians
who would have been installing those 40 years ago than I see in
many of today's electricians.

It is also important to note they offer no protection from direct
contact shocks.

Indeed. Neither should 100mA RCD's be regarded as doing so.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

wrote:

Just because a shock does not actually kill you it does not mean that
you escape unscathed.

Certainly, and this applies to the other causes of death & injury
too.
Death numbers are the one thing we can quantify and compare, so
those are normally what are used for comparison.

What were the figures of deaths if you include appliance related faults?
ISTR the RIA for part P muttered something like 5K before they had to
come clean and admit they had used the wrong stats.

If you look at the top killers, electrocution kills orders of
magnitude
fewer people than a goodly list of other things. I still say spending
your pocket money changing an ELCB to an RCD will give little
safety return compared to addressing other normal household
issues.

These don't have to be "either or" issues - by all means fix the missing
hand rail or lose carpet on the top step *and* fit a RCD.

A smoke alarm in every room would give way more benefit - look at
the govt figures, 70,000 domestic fires a year, 400 annual deaths,

(Tempting to say something about how many of these being caused by
electrical faults is unknown ;-)

Yes again smoke alarms good, interlinked ones better, and mains powered
even better.

and smoke alarms only picking up a percentage of these for
various reasons. From Fire Statistics United Kingdom, 2001,
ODPM:

"A smoke alarm was absent in the fire area in 59% of dwelling fires
in 2001. These fires accounted for around 280 deaths and a further
7,300 non-fatal casualties."

Smoke alarms "failed to operate altogether in 8,100 cases (12%)"

Probably because some muppet had taken the battery out or failed to
replace it.

However its just one more example of solving a problem that isnt
worthwhile.
I don't agree with that as a general statement... you need to take into
account the likely users of the installation, and the uses it will be
put to.

There might be exceptions for unusual uses, but for most of us I
dont think thats the prime issue

If it was a couple of adults in a first floor flat, then there is very
little risk for a RCD to mitigate. A house with kids, or old / infirm
inhabitants plus regular use of power tools in the garden etc then the
picture is different.


--
Cheers,

John.

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On Mon, 25 Feb 2008 11:44:46 +0000, The Natural Philosopher wrote:

If its 30mA you are street legal.However many including myself find that
this gives a lot of nusiance tripping,and I ahve uorated to 100mA on teh
whole board, which dies trip if something really is wrong, but not
otherwise. That means I really OUGHT to get around to putting 30mA trips
on the circuits that feed outside...

AIUI the 100mA trip should be a time delay type to provide discrimination,
otherwise if, say, you cut your hedgetrimmer cable and cause a fault to
earth both your 30mA circuit RCD and 100mA whole house RCD will
probably trip at the same time.


--
John Stumbles

Women always generalise