Clamp meters and 13A Sockets!

[ace]

Hi all!

 

Is it possible to measure the current flowing through a 13A plug with a Clamp meter? I don;t have a clue how this can be done!

 

Thanks..

[Brian]

You need to make yourself an adaptor which lets you put the clamp around just the live wire. Basically a short 13A plug to 13A socket lead but wired in single core cables. BUT make sure you use double insulated cables of the correct size. If you don't know how to do it, get an electrician to do it for you.

[Guest lightnix]

With the clamp meter that I (still) have (for sale - see Classifieds :blink: ) requires an extra widget / lead to measure lower currents flowing through domestic appliances. I'm not certain if this is the case with all clamp meters, but reckon you'll have to spend a fair few quid to get an all singing/dancing one.

[Dave]

Hi,

 

Avo make a thing called a "Flexiclamp 200" that can measure current in a 2 or 3 core cable without having to separate out the live (or neutral) wire in the manner described by Brian. You just clamp the meter round the cable and it does the rest! The only downside is the accuracy for a measurement on a round cable is 12%.

 

If you use it in single-wire mode like a traditional clamp meter, the accuracy improves to a much more respectable 1.5%.

 

And it costs £99+VAT from RS.

 

Dave.

 

P.S. Any ideas as to how it works?? I suspect it uses multiple hall-effect sensors.

[ace]

. Basically a short 13A plug to 13A socket lead but wired in single core cables.

 

Thanks Brian I thought that this would be the solution!

[Ike]

requires an extra widget / lead to measure lower currents flowing through domestic appliances

you could just put a few turns of the live cable through the meter then divide the measured current by the number of turns to get the actual current...well at least I cant see why you couldn't

[ace]

Conclusion!

 

The reason I wanted to do this was really to see how much current I was pulling through a 13A socket with a 6 channel dimmer rack plugged into it. Only out of interest really as it is sometimes fun to see that the figures add up as they say they do, but more to see what actually happened to the current drawn during basic cross fades etc, and to see, for example whether it was possible to get away with 6Kw of light at 50%.

 

Made up a basic adapter (Plug stuck to training socket and sealed with a loop of double insulated wire for the live hanging out! Kinda..) The clamp meter was a cheap £19.99 screwfix one (very impressed for the price).

 

I found that it gave me an acurate reading as to what I expected when loading the rack with lanterns. Ie 1Kw was just under 4A. The reading I got at 50% was about 2A and so the average current was directly proportional.

 

The final test I wanted to see wa how far I could load the rack before either the 13A fuse blew, or the 30ma RCD triped. Supprisingly I was able to load 5Kws on to the 13A socket for an extended amount of time, and the fuse didn't blow - even though the meter was reading 18.1A.. (I only had 5Kw of lanterns to hand) Is this not a really bad thing? or have I missed something?

 

I must have been really bored! :D

[oakwarden]

Conclusion!

 

The reason I wanted to do this was really to see how much current I was pulling through a 13A socket  with a 6 channel dimmer rack plugged into it. Only out of interest really as it is sometimes fun to see that the figures add up as they say they do, but more to see what actually happened to the current drawn during basic cross fades etc, and to see, for example whether it was possible to get away with 6Kw of light at 50%.

 

Made up a basic adapter (Plug stuck to training socket and sealed with a loop of double insulated wire for the live hanging out! Kinda..) The clamp meter was a cheap £19.99 screwfix one (very impressed for the price).

 

I found that it gave me an acurate reading as to what I expected when loading the rack with lanterns. Ie 1Kw was just under 4A. The reading I got at 50% was about 2A and so the average current was directly proportional.

 

The final test I wanted to see wa how far I could load the rack before either the 13A fuse blew, or the 30ma RCD triped. Supprisingly I was able to load 5Kws on to the 13A socket for an extended amount of time, and the fuse didn't blow - even though the meter was reading 18.1A.. (I only had 5Kw of lanterns to hand) Is this not a really bad thing? or have I missed something?

 

I must have been really bored!  :D

The final test I wanted to see wa how far I could load the rack before either the 13A fuse blew, or the 30ma RCD triped. Supprisingly I was able to load 5Kws on to the 13A socket for an extended amount of time, and the fuse didn't blow - even though the meter was reading 18.1A.. (I only had 5Kw of lanterns to hand) Is this not a really bad thing? or have I missed something?

 

A 13A Plug Fuse (BS1362) will carry 13A indefinitely, because thats is what it's rated at. Fuses aren't the best device to use for overload protection as they are generally have a wide tolerance. Looking at a Time/Current plot from the Bussmann website, a 13A fuse will take about 1.6 times rated current without blowing, the curve is an exponential one, so it would blow eventually but after many minutes (or longer), however go to 2 times current and the fuse will blow in 0.11Seconds.

 

 

Into this you will also need to consider, the capability of the plug, its connections and the cable.

 

At 230v 5kW should have given you a current loading of 21.7A by my calculations, is this down to meter accuracy or lack of it?

 

 

At 230v - a resistive load of 3KW will give slightly over 13A - and you may find the plug gets warm at this!

 

the 30ma RCD triped

 

An RCD is protecting against earth leakage - so will only trip when you have an earth fault (a difference between the flow of current down the live and returned via the neutral of more than 30mA), so consequently isn't related to an overload situation.

[Brian]

 

the 30ma RCD tripped

 

An RCD is protecting against earth leakage - so will only trip when you have an earth fault

 

I wonder if what he has is an RCBO - a combined MCB (circuit breaker) and RCD?

 

A 13A Plug Fuse (BS1362) will carry 13A indefinitely

A point which many people overlook. On the other hand, IIRC, a US 13A fuse is rated to blow at 13A.

[ace]

At 230v 5kW should have given you a current loading of 21.7A by my calculations, is this down to meter accuracy or lack of it?

 

I suspect this discrepancy was more likely down to the age of the lamps, or the racks not being all that efficeint?

 

I wasn;t really thinking when I mentioned the RCD, although I did expect the fuse to blow at 13A..

 

You learn somethig new everytime you do something!

[ace]

Just another though.. Does this mean 13A plugs are actually rated to the same current as the fuse?

[techwsussex]

I don't know much about this but...

 

An RCD is protecting against earth leakage

 

Isn't that an ELCB, can someone explain the various different bits and pieces to me?

 

RCD I can't explain, but ELCB, RCCB and MCB I'm fine with.

 

Owen ;) :D

[Brian]

ELCB = Earth Leakage Circuit Breaker. This term should not now be used as strictly speaking it refers to the 'old' way of detecting earth currents. The earth wire of the circuits being protected used to run back to the ELCB where it would feed through a senstive coil, the other side of which connected to the real brown earth. Any fault current flowed through the coil causing it to trip the mains. The problem was that the earth circuit was not continuous (it went through the ELCB) and it had a high resistance, caused by the coil.

 

RCD = Residual Current Device. Works by putting the Live(s) and Neutral through a coil which detects any imbalance in the current flowing out (live) and back (neutral). If there is a difference then that current must be going somewhere where it shouldn't so it trips. These are better as the earth is a nice low resistance continuous circuit.

 

MCB = Minature Circuit Breaker. An overcurrent protection device.

 

RCBO = RCD and MCB in the same lump.

 

RCCB = NRA (Not a Real Acronym)

[adam2]

To return to the O/P, to measure the current in a circuit used from a 13 amp socket, make up an adaptor as earlier described. I have been known to use a coil of ten turns around which the clamp meter is used. Many clamp meters are not very accurate at low currents, and this helps by passing the same current through the clamp meter ten times. Divide the meter reading by ten.

 

Strictly speaking, as has already been said, this should be double insulated wire, though I will admit to use of a piece of single core 2.5mm single insulated conduit cable. I did put this measuring coil in the neutral to reduce the consequences of any damage. If prolonged use rather than a brief test is expected then I would use 2.5mm rather than 1.5mm as ten conductors are in effect bunched together.

 

A 13 amp plug fuse should carry 13 amps continually. they often carry 20 amps for some minutes, but don't count on this.

 

No great accuracy can be expected when calculating the amps used by theatre lanterns or other incandescent lamps. The actual design voltage of the lamps is probably unknown and might be 220 volts, 230 volts, or 240 volts. The actual supply voltage is also probably unknown, and even if measured it may later vary. It could be as low as 200 volts or as high as 254 volts.

 

The actual current used by a lamp may also vary a bit due to manufacturing tolerances, 2% is common, and variances of 5% occur. The running current of a filament lamp also slightly reduces as the lamp ages.

 

 

 

[andy™]

wow... 16 year old thread...

 

a 13a fuse will never blow at 20a either. itll take 22-23a to blow, even that would take minutes. take a look at 1362 time current charts

 

the best & easiest option for those not all that competent with electrics would be to use a plug in adapter that has built in amp / voltage meter etc, save all the hassle of making a lead with individual cores to put a clamp meter around