I've decided that I should add a resistance tester (generically known as a
Megger) to my toolbox and have been surprised at how few there seem to be
available - given that every electrician should(?) have one for testing.

TLC have one for about £80 - can anybody recommend this or another one for
occasional use (2 - 3 times a year)!

Peter

Peter Andrews
wibbled on Tuesday 17 November 2009 17:07

I've decided that I should add a resistance tester (generically known as a
Megger) to my toolbox and have been surprised at how few there seem to be
available - given that every electrician should(?) have one for testing.

TLC have one for about £80 - can anybody recommend this or another one for
occasional use (2 - 3 times a year)!

Peter

Or do you want to do a full range of installation tests as opposed to just
high voltage resistance tests?

If so, then you'll be looking at a Multi Function Tester, or seperate
instruments for:

High voltage resistance tests (you want a 500V test for IEE purposes, some
do 250V and 1000V)

Low ohms impedance test - for measuring L-E and L-N impedances of finished
dead circuits.

RCD tests - measure the trip time and optionally the trip current of RCDs at
various multiples on In (trip rating) and phases (0 or 180 degrees).

Supply impedance test/ PFC test. Optional as you may assume the worst case
values but useful.

Earth rod test - only needed if you have an earth rod (obviously) and not
often found on mainstream multifunction meters.

If you want a basic high voltage resistance test, there are many meters as
you've noticed.

For multifunction, I like the Megger 1552 I have, discount 2nd hand from
ebay. That will still set you back a few hundred though...

If you can clarify and say what your intended use is, I'm sure more opinions
will be forthcoming.

--
Tim Watts

This space intentionally left blank...

On Nov 17, 5:07*pm, "Peter Andrews"
wrote:
I've decided that I should add a resistance tester (generically known as a
Megger) to my toolbox and have been surprised at how few there seem to be
available - given that every electrician should(?) have one for testing.

TLC have one for about £80 - can anybody recommend this or another one for
occasional use (2 - 3 times a year)!

Peter

If you dont need to use it to fill any forms, you can make your own in
minutes for a few quid.


NT

Ebay...
- Robin insulation tester w/continuity test
- Megger rcd tester

Make up...
- Your own wandering lead re R2 figures

You do not need an EFLI (Earth Fault Loop Impedance) tester, you can
calculate Zs from Ze (based on supply type limits) + measure R1+R2.
Unless you have a big welder or large HVAC unit Zs will not likely be
a proble - more important to verify ring/radial continuity and then
resistance is within limits re any bad connections.

If you DO buy an EFLI meter - 1) the non-trip type use a 15mA test
current which will not test corroded armour or steel conduit
continuity adequately (in my view only!) 2) the high current tests use
20-21-25A which will trip an RCD which requires bridging of the RCBO/
RCD.

On balance bothering with an EFLI tester is not important enough. Far
better to do the IR & Continuity + RCD tests, if you use a lot of
power tools & particularly hedge trimmer I would consider an RCD
tester pretty essential. Fluke SM300 will at least test RCD operation
- it's just a resistor to cause a 30mA nominal leakage, it does not
confirm trip trim like a proper tester.

Individual tools are good in that if something fails the replacement
is confined to that tool - repairs can a) be a con re badly done b) be
as much as a new machine certainly on Ebay. Multifunction tools are
favoured because they can record for download later, direct into forms
and so on.

Realise the limits of an IR tester. Air is a perfect insulator - thus
the most grotesquely rotted TRS etc cable will pass quite happily
despite rubber hanging off :-) That is why visual inspection can be
"everything" and why I take IR as a "well it tells me someone trapped
a cable in a floorboard by badly done notching. The best tester is the
RCD tester - Socket and See do some quite cheaply on Ebay, but I
prefer Megger RCDT320. They can be rebadged by electrical factors and
thus very cheap because "it doesn't say megger on it", but is the
exact same machine.

If you have an earth rod, that requires a specialised tester - which
it is useful to have (although cheaper to put a shed on wooden
sleepers and not use Class-1 tools outside :-)

On Tue, 17 Nov 2009 17:07:52 +0000, Peter Andrews wrote:

I've decided that I should add a resistance tester (generically known as
a Megger) to my toolbox and have been surprised at how few there seem to
be available - given that every electrician should(?) have one for
testing.

TLC have one for about £80 - can anybody recommend this or another one
for occasional use (2 - 3 times a year)!

I bought one of these a while ago, and I used it to test all the wiring I
did just prior to Part P. All the insulation and low ohms capability I
needed.

I used a Robin tester for the rest.



--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

On Nov 17, 9:13*pm, John Rumm wrote:
js.b1 wrote:
If you have an earth rod, that requires a specialised tester - which
it is useful to have (although cheaper to put a shed on wooden
sleepers and not use Class-1 tools outside :-)

A standard EL tester will do most earth rods ok - although it does not
test the effect of long duration high current leakages. Having said
that, the system RCDs ought to prevents those from occurring.

Indeed, I was checking around earlier tonight and it appears that
most sparks are just using bog standard EFLI for TT domestic.
Better to whack in another 4ft and use decent Furse etc.

In some ways you could argue that TT is safer with class I tools
outside, since there is little chance of the earth taking on a
potential significantly different from that of the local ground.

That is the point - although there are not many class-1 tools.
Still surprised they do not do 110V hedge trimmers, petrol is
not ideal (ok electric is as noisy) and cordless too wimpy.

Peter Andrews pretended :
I've decided that I should add a resistance tester (generically known as a
Megger) to my toolbox and have been surprised at how few there seem to be
available - given that every electrician should(?) have one for testing.

TLC have one for about £80 - can anybody recommend this or another one for
occasional use (2 - 3 times a year)!

Is this for professional use?

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Nov 17, 9:09*pm, John Rumm wrote:
NT wrote:
On Nov 17, 5:07 pm, "Peter Andrews"
wrote:
I've decided that I should add a resistance tester (generically known as a
Megger) to my toolbox and have been surprised at how few there seem to be
available - given that every electrician should(?) have one for testing.

TLC have one for about £80 - can anybody recommend this or another one for
occasional use (2 - 3 times a year)!

Peter

If you dont need to use it to fill any forms, you can make your own in
minutes for a few quid.

Got a circuit for that?


The overview is that you use a high voltage source, rectify and more
or less smooth it, through a resistor to limit current to a non-lethal
amount, then feed it through a current meter (multimeter) and the
insulation under test. A second meter monitors the test voltage,
though this could be omitted for approximate tests.

An easy cheap source of high voltage is a microwave oven turntable
motor. Hand cranked they produce about 1kV output. Note you need to
use analogue meters with these, digitals cant handle the unsteady
readings.

If you've got nothing better to hand and need to do a job there and
then you can just use the mains to get 330v, or double with a basic
capacitor/diode doubler for 650v, or triple it with a cockroft-walton
for near 1kV. You can also charge up a few big mains lytics to get the
required voltage.

The best option is a battery powered oscillator/transformer, which can
give a steady regulated output at switchable voltages.

Be aware that these testers can produce lethal outputs. Be especially
wary if using a directly mains powered version, it has additional
risks due to lack of isolation.

_Do not_ use crude equipment like this if you dont properly understand
the risks, if youre working professionally, if other people are within
the area served by the wiring under test, or if you're tired or had a
few last night.


NT

On Tue, 17 Nov 2009 19:34:15 -0800 (PST)
NT wrote:

On Nov 17, 9:09Â*pm, John Rumm wrote:
NT wrote:
On Nov 17, 5:07 pm, "Peter Andrews"
wrote:
I've decided that I should add a resistance tester (generically known as a
Megger) to my toolbox and have been surprised at how few there seem to be
available - given that every electrician should(?) have one for testing.

TLC have one for about £80 - can anybody recommend this or another one for
occasional use (2 - 3 times a year)!

Peter

If you dont need to use it to fill any forms, you can make your own in
minutes for a few quid.

Got a circuit for that?


The overview is that you use a high voltage source, rectify and more
or less smooth it, through a resistor to limit current to a non-lethal
amount, then feed it through a current meter (multimeter) and the
insulation under test. A second meter monitors the test voltage,
though this could be omitted for approximate tests.
snip

N

Alternatively, you could do what I did, look on ebay for an old wind-up
megger in a nice leather case complete with probes for about £10.
Works a treat as long as there are no Prat-forms to be filled in. I
can tell if it's under 0.1 ohms, or over 10 meg, but not exactly what
it is, but then who cares (apart from Tony Prat-Prescot).

R.

In article ,
"js.b1" writes:
That is the point - although there are not many class-1 tools.
Still surprised they do not do 110V hedge trimmers, petrol is
not ideal (ok electric is as noisy) and cordless too wimpy.

Who would buy one?
You can't drive a 110V down a long extension lead, so you'd be
lugging around the transformer behind you. Then you've still
got a 240V cable nearby to cut through. I think any conceivable
benefits have evaporated, when an RCD as almost as effective
and a damn sight more convenient.

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

"Owain" wrote in message
...
On 17 Nov, 23:31, Harry Bloomfield wrote:
Peter Andrews pretended :
I've decided that I should add a resistance tester (generically known as
a
Megger) to my toolbox and have been surprised at how few there seem to
be
available - given that every electrician should(?) have one for testing.
TLC have one for about £80 - can anybody recommend this or another one
for
occasional use (2 - 3 times a year)!
Is this for professional use?

It is, but it only needs to develop a few hundred V at a few mA across
a high resistance. That's why there's such a differnce in price
between it and those which also do continuity.

Owain


I think Harry B was asking me if it is for professional use!

The answer is no - just an additional DIY comfort factor and occasional
fault finder (I had to borrow one recently).

Thanks everyone for your comments and advice - I shall ponder upon my
requirements a little longer.

Peter

On Wed, 18 Nov 2009 01:58:18 -0800, Owain wrote:

On 17 Nov, 23:31, Harry Bloomfield wrote:
Peter Andrews pretended :
I've decided that I should add a resistance tester (generically known
as a Megger) to my toolbox and have been surprised at how few there
seem to be available - given that every electrician should(?) have
one for testing. TLC have one for about £80 - can anybody recommend
this or another one for occasional use (2 - 3 times a year)!
Is this for professional use?

It is, but it only needs to develop a few hundred V at a few mA across a
high resistance. That's why there's such a differnce in price between it
and those which also do continuity.

Not quite sure what you mean here. The one I got from TLC does both low
ohms and also insulation tests....

--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

On 18 Nov, 07:43, TheOldFellow wrote:

Alternatively, you could do what I did, look on ebay for an old wind-up
megger in a nice leather case complete with probes for about £10.

Even better, BT test meters (the one with the 500V megohm test
range). Fairly common on eBay and lighter than a wind-up.

I've also had far more failed wind-up meggers (insulation fails) than
I have battery driven ones. Neither survives dropping, as the meter
movement is always going to be fragile, but however well made a 50
year old wind-up looks, you're taking something of a gamble on it
being usable.

"Owain" wrote in message
...
On 18 Nov, 11:13, Bob Eager wrote:
It is, but it only needs to develop a few hundred V at a few mA across a
high resistance. That's why there's such a differnce in price between it
and those which also do continuity.
Not quite sure what you mean here. The one I got from TLC does both low
ohms and also insulation tests....

for £80?

Owain

This is the one that I was looking at:

http://www.tlc-direct.co.uk/Products/TMINS1600.html

Peter

Peter Andrews presented the following explanation :
I think Harry B was asking me if it is for professional use!

The answer is no - just an additional DIY comfort factor and occasional fault
finder (I had to borrow one recently).

Thanks everyone for your comments and advice - I shall ponder upon my
requirements a little longer.

Then it doesn't need to be 17th Edition, or calibrated, so any old
Meggar will do - and much cheaper. I picked up a modern switched
250/500/1000 volt one, with low Ohms range for £15 (intended for my
test bench) earlier in the year.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Wed, 18 Nov 2009 05:54:55 -0800, Owain wrote:

On 18 Nov, 11:13, Bob Eager wrote:
It is, but it only needs to develop a few hundred V at a few mA
across a high resistance. That's why there's such a differnce in
price between it and those which also do continuity.
Not quite sure what you mean here. The one I got from TLC does both low
ohms and also insulation tests....

for £80?

Well, that's what I paid...a little while ago. But it looks the same as
the one the OP posted a link to, and I got mine from TLC. Can't get any
more details...you've reminded me I lent it to someone and I haven't got
it back yet!




--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

On Wed, 18 Nov 2009 14:01:54 +0000, Peter Andrews wrote:

"Owain" wrote in message
news:530f6e96-a1df-4b69-b363-
...
On 18 Nov, 11:13, Bob Eager wrote:
It is, but it only needs to develop a few hundred V at a few mA
across a high resistance. That's why there's such a differnce in
price between it and those which also do continuity.
Not quite sure what you mean here. The one I got from TLC does both low
ohms and also insulation tests....

for £80?

Owain

This is the one that I was looking at:

http://www.tlc-direct.co.uk/Products/TMINS1600.html

That looks exactly like the one I have.

--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

On Wed, 18 Nov 2009 09:47:29 -0800, Owain wrote:

Hmm, 4,2V on the Continuity test, is that for just ringing through
circuits or for testing connections?

I used it to measure the resistance of final ring circuits. And it found
a couple of bad connections!

--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

On Nov 18, 8:32*am, (Andrew Gabriel)
wrote:
You can't drive a 110V down a long extension lead, so you'd be
lugging around the transformer behind you. Then you've still
got a 240V cable nearby to cut through. I think any conceivable
benefits have evaporated, when an RCD as almost as effective
and a damn sight more convenient.

Mmm, argument doesn't work in 3 areas :-)
- 240V to 110V Tx commonplace on building sites
- Plugin RCD dropped and no longer working
- 30mA will still throw you off a metal ladder

However, yes, I do agree that cable length, Tx weight & Tx cost negate
it. One does exist at £250, but add in cable & Tx and petrol wins.

Peter Andrews
wibbled on Wednesday 18 November 2009 14:01


"Owain" wrote in message
...
On 18 Nov, 11:13, Bob Eager wrote:
It is, but it only needs to develop a few hundred V at a few mA across
a high resistance. That's why there's such a differnce in price between
it and those which also do continuity.
Not quite sure what you mean here. The one I got from TLC does both low
ohms and also insulation tests....

for £80?

Owain

This is the one that I was looking at:

http://www.tlc-direct.co.uk/Products/TMINS1600.html

Peter

That looks like the unbranded one we had on my course.

To be honest, it's probably quite adequate for the purpose the OP's stated.

I find stability and accuracy a must on the loop testers ( 1/2 ohm *does*
matter and I wouldn't like to use a cheap unbranded instrument for those)
but for an insulation test, as long as it can *reliably* tell the
difference between 199/299/whatever Megohms at 500V, and a few tens of
Megohms I'd be happy enough.


--
Tim Watts

This space intentionally left blank...

On Wed, 18 Nov 2009 21:29:56 +0000, Tim W wrote:

Peter Andrews
wibbled on Wednesday 18 November 2009 14:01


"Owain" wrote in message
news:530f6e96-a1df-4b69-b363-
...
On 18 Nov, 11:13, Bob Eager wrote:
It is, but it only needs to develop a few hundred V at a few mA
across a high resistance. That's why there's such a differnce in
price between it and those which also do continuity.
Not quite sure what you mean here. The one I got from TLC does both
low ohms and also insulation tests....

for £80?

Owain

This is the one that I was looking at:

http://www.tlc-direct.co.uk/Products/TMINS1600.html

Peter

That looks like the unbranded one we had on my course.

To be honest, it's probably quite adequate for the purpose the OP's
stated.

I find stability and accuracy a must on the loop testers ( 1/2 ohm
*does* matter and I wouldn't like to use a cheap unbranded instrument
for those) but for an insulation test, as long as it can *reliably* tell
the difference between 199/299/whatever Megohms at 500V, and a few tens
of Megohms I'd be happy enough.

Exactly. I have a Robin loop tester...!
--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

In article ,
"js.b1" writes:
On Nov 18, 8:32*am, (Andrew Gabriel)
wrote:
You can't drive a 110V down a long extension lead, so you'd be
lugging around the transformer behind you. Then you've still
got a 240V cable nearby to cut through. I think any conceivable
benefits have evaporated, when an RCD as almost as effective
and a damn sight more convenient.
Mmm, argument doesn't work in 3 areas :-)
- 240V to 110V Tx commonplace on building sites

Hedge cutting on construction sites is normally done with a
bulldozer or digger. 110V isn't common anywhere else.
(Following EU ruling, we can't even insist on it on construction
sites anymore, so that if a French/German/Polish/etc worker
turns up with their 230V tools, they have to be able to use
them unhindered).

- Plugin RCD dropped and no longer working

True, but easily tested, and increasingly socket outlets are
protected anyway.

- 30mA will still throw you off a metal ladder

I cut through cable with mine, tripping the 30mA RCD, and I
didn't feel a thing. (Tip: when cutting the hedge, and a
neighbour waves to you from across the road, don't wave back
with the hedge cutter ;-)

However, yes, I do agree that cable length, Tx weight & Tx cost negate
it. One does exist at £250, but add in cable & Tx and petrol wins.

Professional gardeners all use petrol ones. Having recently
purchased a professional electric cutter, I quickly found
that no one carried any stock of the electric versions - they
had to be a special order from the manufacturer (although
being German, they had a very efficient supply chain and it
only took a few days).

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