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leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
reply to hdman

Re: Turning off Power to a Building

Mistakes happen.

Perhaps phase rotation swaps are more of an issue here since in PG&E territory phase rotation is counter-clockwise (ACB or L1-L3-L2) while most of the US uses clockwise rotation (ABC or L1-L2-L3).
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nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
Reviews:
·Charter
·voip.ms
·surpasshosting

I've seen several scroll compressors (RTUs) fried because the poco restored the phases improperly. I've seen blowers, mixers, and other manufacturing equipment left running backwards by the poco. It happens.
Their typical response: "Not my problem".
Which makes it my problem. And I guess that's good because I could always use more money.
--
If someone refers to herself / himself as a "guru", they probably aren't.



Clever_Proxy
Premium
join:2004-05-14
Villa Park, IL

Okay, now you guys have me curious

After doing a little bit of Googleing, basically 3 phase power is wired in 2 general configurations. Delta and Wye (forgive me if I'm mistaken). Delta has a "high leg" where the power is of higher voltage than the other two legs. Is this what you're referring to when you speak of phase rotation? Is there any way to confirm what the transformer configuration is? The transformers here are pole mounted. I can post pictures.



PSWired

join:2006-03-26
Annapolis, MD

2 recommendations

Delta and wye wiring schemes for 3 phase power are not relevant to phase rotation. AC power is characterized by a voltage that varies continuously in a sinusoidal pattern. 3 phase AC power presents 3 separate voltages, each with the same sinusoidal pattern, but delayed in time with respect to each other:




Phase rotation refers to which of the sinusoids is assigned to each wire in the 3 phase system. When a motor is attached to 3 phase power, the order of these sine waves determines which way the motor spins. So if they're mixed up, the motor will turn the wrong way.

Another common problem is that one of the phases will be disconnected. Equipment like motors will continue to work, but the components for the remaining two phases will be overloaded and could overheat.


Clever_Proxy
Premium
join:2004-05-14
Villa Park, IL

So with that being said, there's no real way for me to check rotation without some decent knowledge and testing equipment?

I guess the easiest and least damage inducing way to test is to power on a device that wouldn't be severely affected by a wrong phase rotation (like one of the 3 phase garage door openers?)



jjoshua
Premium
join:2001-06-01
Scotch Plains, NJ
kudos:3
Reviews:
·Verizon FiOS

1 recommendation

said by Clever_Proxy:

So with that being said, there's no real way for me to check rotation without some decent knowledge and testing equipment?

More like a $25 meter.

»www.ebay.com/itm/T471-Phase-Sequ···91745841


leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
reply to Clever_Proxy

said by Clever_Proxy:

I guess the easiest and least damage inducing way to test is to power on a device that wouldn't be severely affected by a wrong phase rotation (like one of the 3 phase garage door openers?)

If that garage door opener has a properly working overload cutoff then that is an easy and perfectly valid test. It should be pretty obvious when the garage door moves (or tries to move) in the wrong direction.

Edit: before testing the garage door, test a large variety of the single phase loads. It should be obvious if one of the phases is missing because 1/3 of the loads in the building won't work.
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nonymous
Premium
join:2003-09-08
Glendale, AZ
reply to jjoshua

said by jjoshua:

said by Clever_Proxy:

So with that being said, there's no real way for me to check rotation without some decent knowledge and testing equipment?

More like a $25 meter.

»www.ebay.com/itm/T471-Phase-Sequ···91745841

Sure? Someone is worried about how to throw a breaker and you are suggesting they hook up a meter?

Now a question to some of the other posters. Why would the utility return power with a different phase. One poster even said a utility said not their problem and they made cash fixing things.

Ok I was only a utility helper years ago mostly new construction dead plant. But we still did outages for cutovers etc. We hooked everything back up the same as we found it after cutting in the new plant. No random phase shifts etc.


Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

said by nonymous:

Now a question to some of the other posters. Why would the utility return power with a different phase. One poster even said a utility said not their problem and they made cash fixing things.

Ok I was only a utility helper years ago mostly new construction dead plant. But we still did outages for cutovers etc. We hooked everything back up the same as we found it after cutting in the new plant. No random phase shifts etc.

That problem may be true in some states and power companies but in my career I've never heard of Dominion Virginia Power doing it.


leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET

1 recommendation

reply to Clever_Proxy

said by Clever_Proxy:

After doing a little bit of Googleing, basically 3 phase power is wired in 2 general configurations. Delta and Wye (forgive me if I'm mistaken).

So far so good. Delta and Wye are indeed the two ways 3-phase power is wired. Delta simply has 3 phase wires and is more commonly used for power distribution (utility side). Wye also has 3 phase wires but in addition also has a forth wire for neutral. Wye configuration is common at the customer side where the 3 phase power is used since it is capable of providing two voltages (e.g. 120V phase to neutral and 208V phase to phase).

Delta has a "high leg" where the power is of higher voltage than the other two legs.

You only get partial points on this one. Delta 3 phase power comes in a number of varieties (differing in how they are grounded) and what you describe is called either high-leg or wild-leg delta which isn't very common. It is never used for distribution purposes and even for power delivery to the customer it is only used for a 240V delta. In this configuration the center tap of the winding between two phases (A and C) is used as neutral will give you two 120V circuits to the adjacent phases. The opposite phase (B) is only used for 240V 3-phase loads since its voltage to neutral is 208V.

I don't believe the high-leg delta configuration is used in any new installations in the US and some utilities are actively removing existing high-leg delta installations. The main reason is that high-leg delta promotes uneven load distribution across the phases.
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PSWired

join:2006-03-26
Annapolis, MD
reply to nonymous

Mistakes happen, and depending on the value of the equipment connected in that building, it might be worth checking the voltage, phase rotation, etc. before firing everything back up again.

Especially a concern in an old building where wiring and documentation practices have changed and the generation of workers who put the stuff together in the first place has long since retired.



LazMan
Premium
join:2003-03-26
canada
reply to Jack_in_VA

said by Jack_in_VA:

said by nonymous:

Now a question to some of the other posters. Why would the utility return power with a different phase. One poster even said a utility said not their problem and they made cash fixing things.

Ok I was only a utility helper years ago mostly new construction dead plant. But we still did outages for cutovers etc. We hooked everything back up the same as we found it after cutting in the new plant. No random phase shifts etc.

That problem may be true in some states and power companies but in my career I've never heard of Dominion Virginia Power doing it.

I had a case about a year ago or so; where the existing feeds from the utility were "wrong" - and during the maintenance, they "fixed" it for us... Which effectively reversed our rotation.

We got them to un-"fix" it, before we closed the breakers on our side...

Also, several years ago, the local utility at my parents place, crossed up the primary and secondary's when replacing a transformer - destroyed pretty much everything electrical in about a dozen houses; replaced at the utilities expense.

Point is, mistakes happen... linemen are human, too.


leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
reply to nonymous

said by nonymous:

Now a question to some of the other posters. Why would the utility return power with a different phase.

The following doesn't apply to the OP and his utility company because it appears that they are performing proactive maintenance.

The way I understand the problem is that our utility company likes to utilize equipment until it actually fails (instead of proactively replacing aging equipment).

This has some very unfortunate results:
- by the time the equipment fails it is so old that equivalent replacement parts are no longer made and possibly don't even exist in secondary markets.
- because the equipment has failed there is now an urgent requirement to replace it. Therefore even if an exact replacement part exists somewhere, the repair crew will instead take the first available part with suitable specs from the utility yard.
- because the part is different the "just attach it the same way as before" doesn't really apply. It also doesn't help that transformer failure is often accompanied by fire obscuring any markings that may have existed.
- when things are rushed (as in the case of urgently restoring power to a customer) mistakes are more likely.

Having said that and all other failings of PG&E aside, their repair crews are generally very diligent and pay attention to details like phase rotation. I only brought up phase rotation because it is an issue that sometimes happens and the cost for checking phase rotation is very small compared to the potential for harm (which can be very high).
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Clever_Proxy
Premium
join:2004-05-14
Villa Park, IL

1 recommendation

Well everyone, I will say thank you for turning a simple question into a very educational experience.

I opened a disconnect for a forklift charger and found black, red and blue wires. I pulled out a tester and checked it out.
Black to ground resulted 125v
Red to ground resulted 215v
Blue to ground resulted 125v
Tests across two of any legs resulted in 250v

WIth that, I conclude this this is a 240v high-leg delta configuration.

ComEd was out today and I operated all the disconnects. Just as Nunya said, I had to put a little ass into them, but everything operated normally and all of the voltages remained the same post maintenance by ComEd.

Thanks for the info everyone!



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom
reply to LazMan

said by LazMan:

Also, several years ago, the local utility at my parents place, crossed up the primary and secondary's when replacing a transformer - destroyed pretty much everything electrical in about a dozen houses; replaced at the utilities expense.

Point is, mistakes happen... linemen are human, too.

How in the hell does trained electrical workers most likely with a supervisor overseeing the work do that? All of them should have been fired on the spot. That is not a mistake. It's plain incompetence.


cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7

3 recommendations

said by Jack_in_VA:

How in the hell does trained electrical workers most likely with a supervisor overseeing the work do that? All of them should have been fired on the spot. That is not a mistake. It's plain incompetence.

Not everyone can be as awesome as you. Some lesser people have bad days on the job.


Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

2 edits

said by cdru:

said by Jack_in_VA:

How in the hell does trained electrical workers most likely with a supervisor overseeing the work do that? All of them should have been fired on the spot. That is not a mistake. It's plain incompetence.

Not everyone can be as awesome as you. Some lesser people have bad days on the job.

Dude I never had any of my men make such a gross error. To switch the primary and secondary is plain incompetence. Nothing less. There is no such thing as a bad day on the job when dealing with electrical work or anything else for that matter. That's probably the mindset of those causing some of the disasters today.