Electrical Advice please - measuring current drawn

[Summers dad]

Evening folks,

Could anybody advise please, our new building has 3 phase electric and each being 100amps. One sparky has told us if we switch on our new heating we will overload the system, another says that's rubbish. Without collecting all the ratings, is there a meter anybody knows we could attach to the board/main meter to measure max current being drawn to see if we are close to the limit, thanks

[catch21]

You need a clamp meter. It just fits (temporarily) around the incoming cable, one cable at a time. The three phase will probably appear on four cables, three incoming and one outgoing. You need to clamp round each of the incoming in turn,

[Gurmot]

Yes, a clamp meter is what you want. No need to break the circuit to make the measurement although you will probably need to get quite close to potentially dangerous conductors to take the reading.

In practice you will want to measure all 3 live phases individually and use the highest value to calculate how much you have between your existing full load and the 100 amp capacity you say you have. Don't try to measure all three at once as you will get a zero reading due the the alternating currents cancelling each other out. Also. this may not be that straightforward as you will need to ensure existing devices are drawing current. For example, certain items may be controlled by timers or thermostats and not necessarily drawing their full current even though switched on.

Remember to take care and not go anywhere near live conductors. Probably best to get a sparky with a clamp meter to show you and then you can note the measurements.

[aldfort]

Any competent Spark will be able to measure the current on each of the 3 phases.
As has been said you need to make sure the load on each phase is on and represents the likely peak load.
The other thing to check is that you have reasonable load balance on each phase. If you don't it should be easy for a good spark to sort out.

[Summers dad]

Guys, thanks very much for your help.

Before I do anything, im just going to throw (as quickly as possible) my dilema out here and see if anybody has any immediate comments.

I make granite worktops and have just moved into a new yard, I never gave the power a thought but we have 3 phase into the offices each of 100amps. from this board there is a 3 phase supply of 63amp goes to the workshop. In the workshop we have a saw (11kw - estimated 19amps per phase) an edge polisher (18.5kw estimated 31amps per phase) a compressor (11kw estimated 19amps per phase) plus a router pulling 5 amps single phase, lighting and a small 110v system. We seem to be doing fine here.
The problem is due to no gas our plumber has installed a 12kw electric boiler which im guessing will pull 50 amps on a single phase which in theory will blow a fuse if we switch it on. One sparky has refured to wire it up, one has said it would probably be fine.
My own thoughts would be to try and find a way to run the boiler from equally over the 3 phases from the office board which seem to have spare capacity.

I need to start looking at getting an increase in the cable into the building but could anybody advise on A) do my sums look right on the amps per phase and B) could anybody advise on a way to power the boiler using the loads ive calculated are available over the 3 phases using some kind of bridge or onverter.

Thanks very much for taking the time to read this and apologies if ive made a howler somewhere in my calcs, cheers

[Gurmot]

Guys, thanks very much for your help.

Before I do anything, im just going to throw (as quickly as possible) my dilema out here and see if anybody has any immediate comments.

I make granite worktops and have just moved into a new yard, I never gave the power a thought but we have 3 phase into the offices each of 100amps. from this board there is a 3 phase supply of 63amp goes to the workshop. In the workshop we have a saw (11kw - estimated 19amps per phase) an edge polisher (18.5kw estimated 31amps per phase) a compressor (11kw estimated 19amps per phase) plus a router pulling 5 amps single phase, lighting and a small 110v system. We seem to be doing fine here.
The problem is due to no gas our plumber has installed a 12kw electric boiler which im guessing will pull 50 amps on a single phase which in theory will blow a fuse if we switch it on. One sparky has refured to wire it up, one has said it would probably be fine.
My own thoughts would be to try and find a way to run the boiler from equally over the 3 phases from the office board which seem to have spare capacity.

I need to start looking at getting an increase in the cable into the building but could anybody advise on A) do my sums look right on the amps per phase and B) could anybody advise on a way to power the boiler using the loads ive calculated are available over the 3 phases using some kind of bridge or onverter.

Thanks very much for taking the time to read this and apologies if ive made a howler somewhere in my calcs, cheers

Part A. I think you've got your current ratings a little out. For example the full load current on the 18.5kw polisher, assuming it's just a three phase motor may be more like 35 amps but this does depend on the voltage and power factor. That said, this is the full load current so the typical draw may well be less, spending in how heavily it is loaded. The same applies for the other devices if three phase induction motors.

That's the good news though as you may well have starting current in excess of this, particularly with the compressor as this may be being started under heavy load.

Do you use all the equipment at the same time? You may find you will ok if you use the equipment in rotation. If not, you be blowing fuses.

Part B. Have you looked at a calor gas solution?

Edit. do you need a 50kw water heater?

Edit 2. Three phase heaters are available https://www.aquahot.co.uk/water-heat...phase-electric

[mylesm]

you could put a clip on meter connected to a peak hold multimeter and leave it on for a number of days and see what the peak current is as the meter will keep the peak current in its memory and display it this will show max current that was drawn