UK - 3 PHASE ELECTRICAL SUPPLY

[Asjad]

Dear All,

CAN SOMEONE PLEASE HELP:

I am familiar with testing with a single phase appliance, you simply apply
the electrical tester to the live wire
(electrical screwdriver with internal neon light, rated at 240v).

A) Will the electrical tester work for 3 phase (415v)???

B) If I apply a DVM set to AC voltage, between neutral and each individual
phase, will this work??

C) Are there any other methods of testing to see if the 3-phase is entering an appliance without a DVM???

D) I know 3 phase is rated at 415v, what about the potential current that
can be drawn from the supply???


BEST REGARDS!!!

 

[Nigel Goodwin]

Dear All,

CAN SOMEONE PLEASE HELP:

I am familiar with testing with a single phase appliance, you simply apply
the electrical tester to the live wire
(electrical screwdriver with internal neon light, rated at 240v).

A) Will the electrical tester work for 3 phase (415v)???

Yes, you simply test all three lives with it.

B) If I apply a DVM set to AC voltage, between neutral and each individual
phase, will this work??

Yes, but so will a 60W lamp!.

C) Are there any other methods of testing to see if the 3-phase is entering an appliance without a DVM???

See B above!. Or you can buy specific testers, some of which will actually check for the phase difference as well.

D) I know 3 phase is rated at 415v, what about the potential current that
can be drawn from the supply???

It depends on the fuses in the supply, the 415V rating is 'between the phases', each individual phase is 240V. Generally a three phase circuit will allow very heavy loads.

You don't give your country, but in the UK all electricity supplies are three phase - the cable running down a street carries all three phases, but usually only the neutral and one live will be connected to an individual house. In order to balance out the load between the phases, adjacent houses are connected to different phases - this allows them to use a thinner neutral cable, as this only carries the difference between the three loads - so for perfect balance a neutral wire isn't required at all.

If you have a need for higher power you can have a three phase supply installed (it's already there in the street) - but this is usually only required for industrial premises.

Where I work (in a TV service workshop), we have a three phase supply provided into the workshop - although the entire workshop runs off only one of the phases. The three phase was installed when the workshop was built - just in case it might be required in the future.

We have three phase in another part of the building as well, we have a small goods lift for moving heavy items upstairs - and this has a three phase electric motor. This is a good indicator of phase problems, if one phase fails the lift won't work - it just sits and buzzes when you try and use it. The workshop and the rest of the building are on different phases (actually fed from totally different directions) - so it's not unknown for one to have no power, yet the other be OK - although the lift will probably not work.

 

[FoxyRick]

I really think you should take some technician training for this or call in an expert - I have seen (and smelled) 415V burns, they are not nice and the smell makes you sick.

Anyway, to answer your Q's:

A) It will light, but may also burn out quickly, maybe violently if you connect it across the phases by mistake.

B) It might - check the ratings on your DVM (I would not trust a cheap tester at this voltage, even if it says it can do 1000V)

C) **broken link removed** with the 3-phase attachment. See also the end...

D) Current? Far too high for you to make mistakes. Depends entirely on what is supplying it and its internal resistance. For a usual industrial outlet, 100's of amps short-term until a fuse blows.

E) Improvised methods of testing that a voltage is present: Tie two 230V neon indicators together in series, or two small 230V incandescent lamps, and connect between neutral and the phase under test. These will work dimly if correct, and won't blow if you connect them wrong.

Seriously, be careful with 415V 3-phase supplies - you can die quickly or be seriously injured.

FoxyRick.

 

[andrew2022]

A) Will the electrical tester work for 3 phase (415v)???

yes. itll be phase to ground so will never get more than 230V

B) If I apply a DVM set to AC voltage, between neutral and each individual
phase, will this work??

yes, youll get somewhere near 230v. phase to hase will be about 400


C) Are there any other methods of testing to see if the 3-phase is entering an appliance without a DVM???

itll not work if it wasnt. you can get non-contact testers altho theyll light up even if there is only 1 or 2 phases live. only real way for that is direct contact

D) I know 3 phase is rated at 415v, what about the potential current that
can be drawn from the supply???

depending on how far away you are from the tansformer and the cables resistance, potentially thousands