Live 480V buss ties on switchgear

[powerpete69]

Gents,
It is my understanding that the industry is moving away from doing live 480V bus ties on Switchgear. Due to NFPA, OSHA and so forth.
It is also my understanding that some sites are not in phase and live buss tieing can be very dangerous in this condition.
My current switchgear contractor just emailed me and told me they are no longer allowed to do it.
So this is all very understandable.

However, my site has 40 substations that were built for live bus tieing. My maintenance guy has been closing bus ties out here for 40 years without incident. They even practice closing live 480V bus ties on a monthly basis to train people. ON several occasions they have even closed EVERY single buss tie on site....with all 40 of our 4160V breakers fully closed. All bus ties perform flawlessly, in perfect phase.

So although this rule is good for most, I don't see how it applies to my site. I feel there is an exception here.
If this rule is actually infused, We will likely have 3 times the amount of shutdowns per year costing big money in production. (no one likes losing money)

What are other people doing in regards to this assuming you have the same in phase switching that I have? Oh ya, our guys ALWAYS wear the full 40 calorie moon suit when switching anything in our switchgear.

I realize this is a touchy subject for the moderators, but I believe it is one that should be openly discussed.

 

[jim dungar]

What do you mean by 'live buds tie'?
Simply closing a breaker?
Racking a breaker into position then closing it?
Installing a removed breaker into position then closing it?
This is MV so I assume you do not mean physically touching bus bar links.

 

[hillbilly1]

You can still do live work, but you just better have a good reason if something goes sideways.

 

[powerpete69]

What do you mean by 'live buds tie'?
Simply closing a breaker?
Racking a breaker into position then closing it?
Installing a removed breaker into position then closing it?
This is MV so I assume you do not mean physically touching bus bar links.

I mean tieing one substaton to the other thru their 480V tie breakers.
For example, if I need to work on a 5KV switch on said substation, instead of killlng the whole substation, I can close its 480V tie breaker to other substation 480V tie breaker live. (close both 480 V tie breakers, one...then the other) Then I can then open (lock out) the main 4160V breaker feeding substation.....then open (lock out) the main breaker on that substation.....which will completey de-energize 5KV switch and transformer thru lock out points while leave that substtaion fully energized thru its bus tie. We have done this for 75 years on site without incident. Everytihng is in phase!

 

[powerpete69]

I guess what I'm trying to ask is this:
Where does it specifically say in 70E or OSHA that you can NOT live bus tie two 480V TIE breakers that are in phase?

At this point, I really need to think about court....litigation...and so forth. So that's why I want to know the exact rule.

 

[ron]

I believe when you say live bus ties, you mean closed transition across tie breakers.

There is no rule against it. If the SWBDs or SWGR are properly rated for short circuit current during the closed transition and the doors are closed, there is no problem.

 

[smoothops10]

It may not be cheap but a protective relay with IEEE/ANSI 25 function may help you sleep at night if there is a chance the substations with "everything is in phase" is possible to ever be out of phase for whatever future reason. Set it up to work as an inhibit preventing the breaker closure when the other is closed if Sync-check is not true.

IEEE Device Number 25 Sync-check:
Synchronizing or synchronism-check relay. A synchronizing device that produces an
output that causes closure at zero phase angle difference between two circuits. It may or
may not include voltage and speed control. A sync-check relay permits the paralleling of
two circuits that are within prescribed limits of voltage magnitude, phase angle, and
frequency.

This is being used for interconnecting distributed resources/generators when paralleled with utility supply.

 

[jim dungar]

You are typically allowed, under NFPA 70E and OSHA, to operate properly maintained circuit breakers even if it is to close bus ties.

Many companies have also employed remote breaker operating switches for these cases.

 

[powerpete69]

I believe when you say live bus ties, you mean closed transition across tie breakers.

There is no rule against it. If the SWBDs or SWGR are properly rated for short circuit current during the closed transition and the doors are closed, there is no problem.

What do you mean by "if the doors are closed"? I have to open the front door on the switchgear to get to the breaker handle. The face of the breaker is completely closed however. There are the typical "file cabinet" breakers. The breaker face stays completely closed while opening and closing breaker. We also use brand new AC pros on everything for relays.

The reason I call it live bus tie is because the substation is live when bus tieing. The ultra safe way is too de-energize both subs and then close the tie breakers. This causes line shutdowns and loss of money tho.

 

[ron]

What do you mean by "if the doors are closed"? I have to open the front door on the switchgear to get to the breaker handle. The face of the breaker is completely closed however. There are the typical "file cabinet" breakers. The breaker face stays completely closed while opening and closing breaker. We also use brand new AC pros on everything for relays.

The reason I call it live bus tie is because the substation is live when bus tieing. The ultra safe way is too de-energize both subs and then close the tie breakers. This causes line shutdowns and loss of money tho.

NFPA 70E Table 130.5(C) Estimate of the Likelihood of Occurrence of an Arc Flash Incident for ac and dc Systems indicates that Operation of a CB, switch, contactor, or starter, with normal equipment conditions has no likelihood of an arc flash occurrence. This typically means the doors closed.
If there are any racking of the breakers of CBs from cubicles in an abnormal equipment condition, there is a likelihood of an arc flash occurrence.

 

[jim dungar]

The phrase 'doors closed' is ambiguous.

50 years ago there were breaker designs that required you to open the cubicle door in order to operate them. You could see, and even touch, parts of the breaker operating mechanism. Most Electrical Safe Work Practice programs frown on operating these with the door open, resulting a market for remote controlled operating motors and assemblies for racking and closing.

These are often confused with the breaker style the OP described as a 'file cabinet', like the Westinghouse DS breaker. These had doors covering the breaker cell, kind of like a door on a panelboard. Some people have upgraded these breakers to have motor operators, thus allowing remote operation, although racking is still an issue

Current versions of this switchgear no longer have any doors covering the breakers at all. Some even have removable motor operators that provide for remote racking.

 

[D. Castor]

AFAIK, there is nothing in NFPA 70E that would automatically prohibit this. Once a facility is commissioned, there is normally little chance of a phasing issue at the 480 V level. A bigger concern is usually the increase in the available 480 V fault current when the two transformers are paralleled. This can often exceed the short circuit rating of the breakers, since the fault current will nearly double. If the breaker short circuit ratings are exceeded, this would be violation of the NEC and NFPA 70E, as well as the manufacturer's instructions.

Hot transfers are pretty common. Electrically-operated breakers make it much safer.

 

[powerpete69]

AFAIK, there is nothing in NFPA 70E that would automatically prohibit this. Once a facility is commissioned, there is normally little chance of a phasing issue at the 480 V level. A bigger concern is usually the increase in the available 480 V fault current when the two transformers are paralleled. This can often exceed the short circuit rating of the breakers, since the fault current will nearly double. If the breaker short circuit ratings are exceeded, this would be violation of the NEC and NFPA 70E, as well as the manufacturer's instructions.

Hot transfers are pretty common. Electrically-operated breakers make it much safer.

I would definitely agree that double checking the short circuit ratings (in easypower model) with both tie breakers in closed position with both transformers hot would be most wise.

 

[Jraef]

It is my understanding that the industry is moving away from doing live 480V bus ties on Switchgear. Due to NFPA, OSHA and so forth.

To this first point, I have never heard this. I know of no NFPA/OSHA rules that would prohibit this. Someone would have to show that to me if they are standing on that statement.

It is also my understanding that some sites are not in phase and live buss tieing can be very dangerous in this condition.

The only way they would not be in phase is if they had site generators or maybe an inverter that are not synched up to the utility grid, in which case you absolutely would not close a tie breaker. But why would you want to do that in the first place? Side note: inverters used in NEM systems must synch to the grid, so that possibility is remote.

My current switchgear contractor just emailed me and told me they are no longer allowed to do it.

I would find a new contractor. Sounds to me like someone is over thinking something…