Hello All,

As I try my best to describe the situation in the title, I have a project that I need to setup a A/V rack in an industry building. In the very beginning of my project I found one of the 3 phase circuit breaker boxes provides no power. Since it leads to the closest socket I can use I meant to find out why and gather more information before I talk to my client about the issue. I did some basic measurement, checked all the circuit breaker, and finally I turned off all the individual circuit breakers and focused on the main switch which has three leads and a ground connection. L1 to L2, L1 to ground, L2 to ground, all measured 220V, on the other hand L3 measure no voltage. That cable came directly from outside.

Q1. is it safe to say that there's problem from the floor's or building's former room?

Q2. My colleague suggests that we should just swap the cable to get power from one of the other two phase, as long as we're sure the power consumption is within safety range, do you agree?

PS. obviously i'm from the other planet and not a pro, thank you so much for bearing with me, and thank you so much for your advice, much appreciated. Let me know if you think I should provide more info.

 

Who responsibility or jurisdiction does the external supply (3ph Transformer?) come under?
If the service provider, advise them there is a possible problem.
Or track down the source of the 3phase, presumably it IS 3phase, another possiblility it is a 3ph delta and the 3rd phase is grounded as a Earth reference.
Max.

 

and focused on the main switch which has three leads and a ground connection

It is a 3P+1N circuit breaker. It will have 6 contacts, 4 inputs and 4 outputs.

3 Phase + 1 Neutral.

Out of 3 Phases one Phase has failed. Maybe the fuse used for that phase has blown.

 

Who responsibility or jurisdiction does the external supply (3ph Transformer?) come under?
If the service provider, advise them there is a possible problem.
Or track down the source of the 3phase, presumably it IS 3phase, another possiblility it is a 3ph delta and the 3rd phase is grounded as a Earth reference.
Max.

Hello Max, if I didn't understand wrong, you mean that phase was designed not to provide power, but it is currently connected to a few lights and wall panels.

i'll need to talk to my client and let him find out who's responsible, it's gonna be a painful process. He will have to contact his client, and his client may need to contact the power company or the landlord... omg...

It is a 3P+1N circuit breaker. It will have 6 contacts, 4 inputs and 4 outputs.

3 Phase + 1 Neutral.

Out of 3 Phases one Phase has failed. Maybe the fuse used for that phase has blown.

thank you for your reply, yes, it is exactly what you describe. Do you mean that there should be another fuse box somewhere in the building? That I maybe able to ask the building's management office to check. But I have to apologize for being inaccurate, it measured low voltage, around 4V, not completely dead.

 

thank you for your reply, yes, it is exactly what you describe. Do you mean that there should be another fuse box somewhere in the building? That I maybe able to ask the building's management office to check. But I have to apologize for being inaccurate, it measured low voltage, around 4V, not completely dead.

If 4V then fuse will be ok. Maybe a brown out with that Phase. You have to contact electricity department (one you supplies power) to check if 3 Phase power transformer is ok.

Does the building also have solar power supply installed and supplying power to grid ?

 

Some low voltage distribution systems ground phase 3. It sounds like this is the case because all your phase to phase voltage measurements are equal. The reason for this is that the transformer has a delta connected secondary rather than Y connected where the center of the Y is grounded. Grounding phase 3 avoids the expense of adding a delta-Y zig-zag grounding transformer.

 

Some low voltage distribution systems ground phase 3. It sounds like this is the case because all your phase to phase voltage measurements are equal. The reason for this is that the transformer has a delta connected secondary rather than Y connected where the center of the Y is grounded. Grounding phase 3 avoids the expense of adding a delta-Y zig-zag grounding transformer.

If that is the case then what is the use a getting a 3-Phase Power supply if one Phase doesn't provide power ? If a building needs more power then how to get it when the other two Phases can't provide it ?

 

If that is the case then what is the use a getting a 3-Phase Power supply if one Phase doesn't provide power ? If a building needs more power then how to get it when the other two Phases can't provide it ?

Of course it provides power, it is a 3rd phase, just that one is referenced to Earth ground.
Ignoring the grounded phase, it works like any other delta secondary.

@thom kurt
But the fact there is 3 breakers probably it is not this configuration this time.
If it involves a lot of red tape to find out, maybe just a call to the local provider may be possible to get an answer or at least a suggestion.
If a large industrial building, they are going to have their own sub-station, power house or room for all incoming power.
There are not typically individual 3ph breakers, one trips, the other two trip.
P.S. Where are you located?
Max.

 

If 4V then fuse will be ok. Maybe a brown out with that Phase. You have to contact electricity department (one you supplies power) to check if 3 Phase power transformer is ok.

Does the building also have solar power supply installed and supplying power to grid ?

A few calls and a trip down the building's office are unavoidable. In terms of solar power, they're rarely seen in traditional industry building like this one.

Some low voltage distribution systems ground phase 3. It sounds like this is the case because all your phase to phase voltage measurements are equal. The reason for this is that the transformer has a delta connected secondary rather than Y connected where the center of the Y is grounded. Grounding phase 3 avoids the expense of adding a delta-Y zig-zag grounding transformer.

it has to be mentioned that phase to phase only measured equal without loading.

Of course it provides power, it is a 3rd phase, just that one is referenced to Earth ground.
Ignoring the grounded phase, it works like any other delta secondary.

@thom kurt
But the fact there is 3 breakers probably it is not this configuration this time.
If it involves a lot of red tape to find out, maybe just a call to the local provider may be possible to get an answer or at least a suggestion.
If a large industrial building, they are going to have their own sub-station, power house or room for all incoming power.
There are not typically individual breakers, one trips, the other two trip.
P.S. Where are you located?

It's just that I don't have enough knowledge to understand the whole picture, except from everything lil piece of info I learnt from this forum, the other two phase working just fine, there're alot going on in other rooms, drilling and everything, all i got was 15min alone with my small meter, tested all phase to phase and phase to neutral voltage, and the neutral alone, I wanted to test is there a short or something without cutting open anything...

I'm from Hong Kong btw.
Max.

 

I assume you checked the input side of the breakers?
I would imagine that H.K. has a same or similar system to UK, maybe, due to the History.
Max.

 

Does the A/V systems draw enough power to actually need a full three phase feed source?

 

My best suggestion is you need to find out exactly what the service should be. Anything else is guesswork and speculation. While I have done quite a bit with three phase industrial power I have never seen an instance where a neutral line or ground line was fused or run through a breaker. Matter of fact I have never seen a neutral or ground switched. Anyway, point being you need to find out exactly what you have and should be looking at. That is where I would start anyway.

Ron

 

Hence a call to the service provider!
Max.

 

Hence a call to the service provider!
Max.

Bingo!

Ron

 

One of the first things I did in a industrial building or complex, was to seek out someone or somebody that looked after general day to day building maintenance, they may not have come with any kind of extraordinary technical ability, but at least they knew where everything was, and if there was a sub-station or at least a locked-off room where the high voltage came into for local distribution, or at least if there was any other anomaly happening in any part of the building/complex.
As already suggested, do you need 3phase? Also do you require a grounded neutral for the equipment?
Max.

 

L1 to L2, L1 to ground, L2 to ground, all measured 220V,

Am I missing something? These numbers can't all be right, can they? I'm a familiar with a few three phase systems, including high-leg delta, but I can't wrap my head around any system where L1 and L2 are both 220V to ground, but there's also 220V between them.

UPDATE: A little playing around in LTspice showed me that a 60 degree phase difference between the legs would explain those voltage readings. Still, I've never heard of a distribution system with two phases 60 degrees apart.

 

This also points to the H.K. Electical distribution system similar to UK.
https://www.hkelectric.com/en/custo...r/setting-up-business-in-hk-about-electricity
Max.

 

This also points to the H.K. Electical distribution system similar to UK.
https://www.hkelectric.com/en/custo...r/setting-up-business-in-hk-about-electricity
Max.

Wouldn't HK power read 380 between L1 and L2? The thread starter reports 220 L1 to L2. That's the part that seems bizarre to me.

 

I assume you checked the input side of the breakers?
I would imagine that H.K. has a same or similar system to UK, maybe, due to the History.
Max.

precisely, we still follow BS, and yes, I measured the inputs, that's the set of cable directly came from out side of the whole flat.

 

Does the A/V systems draw enough power to actually need a full three phase feed source?

that I can't answer, we will approximately draw 24A in total, which I already divided by 0.8

We usually will put audio and video in two groups, each will be drawing power from a 30A breaker.