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nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
reply to LazMan

Re: Turning off Power to a Building

I think you replied to the wrong person. I didn't say anything about arc flash.
--
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LazMan
Premium
join:2003-03-26
canada

I know you didn't bring it up - I was asking if it's becoming an issue for you guys; the same way it's become a pain in the ass up here.



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

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.


nonymous
Premium
join:2003-09-08
Glendale, AZ
reply to Jack_in_VA

said by Jack_in_VA:

said by LazMan:

Just to duck out on a bit of a tangent - are you guys not jumping on the Arc-Flash bandwagon down there?

I now have to have exclusion zone's marked on the floor, and need to wear a suit to operate anything 600v or higher; or 100A or larger.

More Big Brother. I worked in industry for 35 years before retiring and the thousands of MCC starter buckets, 2300 v starters, 4160 v starters and 15 kv switchgear and transformers never once did we ever have an "arc-flash" and we worked a lot of the 480 volt gear hot. The key is to have qualified trained Electricians to do the work.

The damn suits are a sick joke mandated by a government agency whose inept employees are clueless but have unaccountable power.

maybe no arc flash suits but probably say cotton work clothes not nylon or polyesters leisure suit to melt into skin even with a small error.


PSWired

join:2006-03-26
Annapolis, MD

2 recommendations

reply to Clever_Proxy

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?)



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

said by nonymous:

said by Jack_in_VA:

said by LazMan:

Just to duck out on a bit of a tangent - are you guys not jumping on the Arc-Flash bandwagon down there?

I now have to have exclusion zone's marked on the floor, and need to wear a suit to operate anything 600v or higher; or 100A or larger.

More Big Brother. I worked in industry for 35 years before retiring and the thousands of MCC starter buckets, 2300 v starters, 4160 v starters and 15 kv switchgear and transformers never once did we ever have an "arc-flash" and we worked a lot of the 480 volt gear hot. The key is to have qualified trained Electricians to do the work.

The damn suits are a sick joke mandated by a government agency whose inept employees are clueless but have unaccountable power.

maybe no arc flash suits but probably say cotton work clothes not nylon or polyesters leisure suit to melt into skin even with a small error.

We required cotton work uniforms and safety glasses


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

1 recommendation

reply to Clever_Proxy

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:9
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:9
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:9
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.


Red_Menace
poking around since 1978

join:2001-11-03
Littleton, CO
reply to LazMan

Yep, definitely a pain in the ass. I mainly do controls, and the last couple of employers had a "no hot work" policy - of course, you needed to use hot gloves, shields, suits if needed, etc, just to check if you couldn't work on something.

I've also worked in a few production environments, but haven't come across any that would allow panels to be shut off (ever), even though their own safety policy doesn't allow hot work. Nice.

Can't wait to retire - it's no fun anymore.



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

said by Red_Menace:

I've also worked in a few production environments, but haven't come across any that would allow panels to be shut off (ever), even though their own safety policy doesn't allow hot work. Nice.

Very familiar with that. When you consider what it costs a manufacturer to shut down a process it's very understandable to require the work to be done hot.


DarkLogix
Texan and Proud
Premium
join:2008-10-23
Baytown, TX
kudos:3

2 edits
reply to Clever_Proxy

said by Clever_Proxy:

I have a question for the electricians out there. I have a building that has an industrial 3 phase coming into it. The local utility company out here is going to be performing work on the transformers that feed the building directly. They told us to turn off the power to prevent damage to any of our equipment during the work.

Is there any danger to myself and the building by throwing these switches? I know enough about electricity to be dangerous and that's about it.

I'd turn off the lower load ones first.

I know that at a place I worked previously the head electrician got hospitalized when he turned off one of the large breakers that still had a high load on it (a huge arc occurred and burned his arm very badly)

Learn what feeds what and I would work my way from the breakers just after the normal looking ones up to the main.

Also Hope that the Main is labeled (at another place I worked they turned off all 3 mains, it has 3 sets of 3 phase power coming in at 980v, and I had to hunt for the one that powered the server room) (along with the lesser breakers leading to the panel that feed the transformer that feed the panel that feed the server room)(they had 480v distro through the building with a 3 phase transformer feeding a panel that powered the office area)(Ya it took some time to map out the path from server room to master breaker and did it by flashlight)
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