In message , Alan
writes
In message , raden
wrote
In message , Alan
writes
In message , "Dave Plowman (News)"
wrote


I've got some ways of calibrating DVMs,

While you may have some accurate ways of calibrating (or checking the
calibration of) a multi-meter I guess the average electrician
doesn't. Was that resistance measurement really 2 ohms or was it
actually 4 ohms but with a partially fried ranging component?

How often would a sparkie want to measure more than whether 230V was
there or not with a DVM ?


Do you mean that they don't actually do earth bonding tests etc. It may
not be performed with the £4 LIdl special offer DVM but it should be
with equipment that is calibrated if they are going to issue a
certificate saying that the installation is safe..




How many of them would even know to null out the resistance of the
probes ?


--
geoff

In message , Jim Michaels
writes
For some reason the Maplin's person on the phone told
me this had a voltage rating of 60V, whereas it's
actually 250V.

I'm not an expert on fuses, but the fuse rating is a function of current
and time. Although most 20mm fuses I see are 250v rated, I don't see the
relevance, especially if it's hidden inside a multimeter

The 250V is the maximum that the fuse is rated to break.

At voltages above it's rating a fuse may arc and continue to pass
current instead of opening and clearing the fault.

If a 32V fuse (as used in cars) is fitted, the meter is set to
current, the leads are connected across 240V, and the fuse did not
clear but arced, serious personal injury or death could result.


Err ... how exactly ?

If you're measuring something with a DVM, you're only either touching
the probes and/or the dial. The fuse is there to protect the DMM guts

--
geoff

On Wed, 14 Sep 2005 19:52:21 GMT, raden scrawled:

If a 32V fuse (as used in cars) is fitted, the meter is set to
current, the leads are connected across 240V, and the fuse did not
clear but arced, serious personal injury or death could result.


Err ... how exactly ?

If you're measuring something with a DVM, you're only either touching
the probes and/or the dial. The fuse is there to protect the DMM guts

Which could explode and kill and\or mame humans in the vicinity if the
correct fuse isn't fitted, possibly.....
--
Stuart @ SJW Electrical

Please Reply to group

In message , Lurch
writes
On Wed, 14 Sep 2005 19:52:21 GMT, raden scrawled:

If a 32V fuse (as used in cars) is fitted, the meter is set to
current, the leads are connected across 240V, and the fuse did not
clear but arced, serious personal injury or death could result.


Err ... how exactly ?

If you're measuring something with a DVM, you're only either touching
the probes and/or the dial. The fuse is there to protect the DMM guts

Which could explode and kill and\or mame humans in the vicinity if the
correct fuse isn't fitted, possibly.....

Yeah - inside a DVM case - really

it's not a bloody landmine, it's a glass tube, stuck inside a plastic
case

--
geoff

On Thu, 15 Sep 2005 02:21:26 -0500, Jim Michaels wrote:

For more information...

http://www.ferret.com.au/articles/ca/0c02ebca.asp
http://www.arcadvisor.com/faq/what_a...h_hazards.html

"Exposure to an arc flash frequently results in a variety of serious
injuries such as severe burns, damaged eyesight, ruptured eardrums,
collapsed lungs and in some cases fatal death."

Er, is that worse than non-fatal death, then?

On Thu, 15 Sep 2005 02:21:26 -0500, Jim Michaels wrote:


When checking out a meter tail.

240V x 5,000a = 1.2 MegaJoules/second.

This is equal to 409grams of TNT exploding per second.

Which is equal to a Claymore Landmine exploding every 1.6 seconds.

When I worked in central London many years ago there was once an explosion
in South Kensington that was at first thought to be the work of the IRA,
but turned out to be an explosion in an electricity cable buried below a
pavement. The blast flung paving slabs across the road and broke plate
glass windows in shops nearby.