Voltage drop

[Jackie]

Just thought I would ask on the chance that someone knows about the French digital electricity meter and differential trip units, and whatever else is in the box with the lead seals.

 Whilst doing some wiring I noticed that the volts across the two tails coming into the consumer unit take quite a drop when a load is switched on in the house. About 5 volts for each 2 kilowatt load switched on. I find it difficult to believe that this is a drop caused by the current flowing through the overhead cables feeding the house though I suppose it is possible and we may be at the end of a very long line. The only other possibility is a drop in the meter/AD TOO/Disjoncteur Differentiel unit but that is also difficult to believe as with all those watts being dissipated you would have expected it to get rather hot and this does not happen!

So what resistance could you expect between the incoming power cables and the feed to the consumer unit? I cannot get a voltage measurement across the incoming cables for obvious reasons. Any thoughts on how to identify the source of this drop anyone? We have a 9kVA supply………………………………………John not Jackie

[Punch]

It seems to me from your description that is highly likely that it is caused by either the cross sectional size of the incoming EDF wires, or the distance you are from the nearest EDF transformer, or a combination of both. I have EDF meetings and this is a common problem. You can measure the voltage at the outgoing terminals of your disjoncteur to see what voltage you have incoming. This may not tell the true story because the voltage may drop further when other people draw power. Quite often if you are at the end of a long run, this will be a problem especially when every one else on the line before you switches on their heavy appliances or machinery.

Paul

 

[Jackie]

Thanks Paul. I have had a look at volts on the terminals of the disjoncteur. The drop is as reported.

Where do the two thick wires go after this, the consumer unit or some other part of the meter/AD TOO/Disjoncteur Differentiel unit as they don't seem to be the same colour as the wires coming into the consumer unit. The wires feeding the consumer unit are red and blue whereas the wires seen in the bottom section of the disjoncteur are black and blue. In other words where is the disjoncteur positioned electrically, on the incoming wires to the house or after the meter unit? I would be surprised if before as it would be too easy to bypass the meter! There is a lead seal on the top section of the disjoncteur but not on the bottom cover which I removed.

I take your point about volts drop on the external line. We are at the end of this line with two other houses and I have not seen a transformer unit around here anywhere. Thanks for your reply........................................John 

[Punch]

The EDF disjoncteur comes after the EDF meter and fuses, and the outgoing terminals usually should go straight to the consumer unit, but often divert off to a junction box beforehand, which is what i suspect you have. Difficult to diagnose without seeing but I would switch off and then have a good look around. 

 

Paul

[Jackie]

Ok Paul I will do just that and many thanks again................................John

[Dave&Olive]

ok all you experts out there work this out ... we have a 3 phase supply at 15amps per phase the machine i am trying to run drags 16 amps under full load . Plugged her in to try bang blew the fuse , ok the fuse was 10amp going to get slatted for this but fitted 20amp fuse wire just for the test all the lights went dim on start up but she ran ok , but i need to run a dust extracter with it , found out the water heater socket has a 20amp fuse on its own circuit so plugged the extension lead in to it to run the above when i start he up the lights now glow bright for a few secs on start up .......voltage drop or ?????

                   dave

[Punch]

If you don't kill yourself first, you will probably burn your house down judging by the experimental way you are playing with three phase electricity. Do you know what terminals are what on the 20 amp socket, it sounds like you have overvoltage and I would get an expert in  before you do any damage, like melt any hidden wiring....................;

Paul

[Punch]

If you don't kill yourself first, you will probably burn your house down judging by the experimental way you are playing with three phase electricity.

The fuses blow due to the start current you get with three phase motors which is lower than the running current. You should never use fuse wire for motor protection.

Do you know what terminals are what on the 20 amp socket, it sounds like you have overvoltage and I would get an expert in  before you do any damage, like melt any hidden wiring....................;

Paul

[Nick Trollope]

Dave,

Heed Paul's valuable advice!!

But, are you sure that your machine is 15HP? (16A three phase, about 12kW). If it isn't, then you have another problem.

 

[Dave&Olive]

hang on a mow , read the post first before you screwfix direct sparkies jump in , never said it was 3 phase ,the machine is single phase but drags 16 amps under full load so read the question again and then reply .

oh I do have a t4 city and guilds in elec/mech engineering  so do not talk to me like a prat

           love dave

[Deimos]

Without wanting to hijack this thread, but; I have a three phase supply to the house and the “master breaker” device (old box with a small black and a small red button on it that seems to disconnect the house from EDF). This box has a small plastic window with something saying “20” inside. Am I correct in assuming that this means I have 20A on each phase (i.e. absolute may of 60A on all 3 phases, but each phase limited to 20A) ?

Many thanks

Ian