400 Amp Safety Switch Tripping

[ryanpickett2003]

I have a 3 phase 400 amp service. The service consist of a 400 amp indoor panel with main breaker. On the outide, there is a fused safety switch next to a bolt in meter. About 3 weeks ago the shopping center had a power outage that tripped the safety switch. I was called back out this morning and the safety switch was tripped again. The owner told me this was the third time in 10 days. The business is a laundry mat and the only time it is tripping is during the night, when little load is present. I checked the safety switch and everything looks great. Any suggestions on what could be the problem. Thanks.

 

[texie]

I have a 3 phase 400 amp service. The service consist of a 400 amp indoor panel with main breaker. On the outide, there is a fused safety switch next to a bolt in meter. About 3 weeks ago the shopping center had a power outage that tripped the safety switch. I was called back out this morning and the safety switch was tripped again. The owner told me this was the third time in 10 days. The business is a laundry mat and the only time it is tripping is during the night, when little load is present. I checked the safety switch and everything looks great. Any suggestions on what could be the problem. Thanks.

Possible intermittant fault on the feeder-seen it before. Since you have fuses you can saw the blown one open and possibly tell if it opened due to short circuit or overload.

 

[ryanpickett2003]

None of the fuses have blown. They are the orginal fuses. The inside panel is directly behind the safety switch.

 

[texie]

None of the fuses have blown. They are the orginal fuses. The inside panel is directly behind the safety switch.

I'm confused. You said the safety switch "tripped". I took that to mean the fuse blew. Maybe you are saying that the MB in the panel tripped? If so, obviously my advice is moot.

 

[ryanpickett2003]

I see we are on the same page. No breaker has tripped or fuse blown. The safety switch handle will be in the halfway position. I reset it and pust it back on and it will work until who knows when. It makes no sense to me or anyone else I've talked to today. My problem is I have a owner who keeps calling me and I haven't got an anwser. Doesn't make me look very good.

 

[texie]

I see we are on the same page. No breaker has tripped or fuse blown. The safety switch handle will be in the halfway position. I reset it and pust it back on and it will work until who knows when. It makes no sense to me or anyone else I've talked to today. My problem is I have a owner who keeps calling me and I haven't got an anwser. Doesn't make me look very good.

Maybe somebody is screwing with it as a prank/disgruntled worker. With the old knife type switches of this size this is possible to leave it in a partial position. Maybe you could padlock it in the on position-it's legal to do so.

 

[GoldDigger]

I see we are on the same page. No breaker has tripped or fuse blown. The safety switch handle will be in the halfway position. I reset it and pust it back on and it will work until who knows when. It makes no sense to me or anyone else I've talked to today. My problem is I have a owner who keeps calling me and I haven't got an anwser. Doesn't make me look very good.

How much friction is holding the switch in the closed position? Is it a simple knife switch or are there over-center springs to force it one way or the other once you move it partway? Possibly there is a mechanical failure and the springs are actually pushing it open the whole time and just the contact friction is holding it closed?
"Reset it and push it back on" sounds a lot more like a breaker than a switch.

 

[ptonsparky]

Are you referring to a fused service disconnect as a safety switch? The handle of the fused disconnect is down? Safety switches do not just fall open. They need help or are in very poor operating condition visible from several feet away.

Or.

The circuit breaker has tripped and you must turn it off to reset, then back on?

Go back later in the day and check to see if feels hot. Do a FOP test.

 

[jeremysterling]

How much friction is holding the switch in the closed position? Is it a simple knife switch or are there over-center springs to force it one way or the other once you move it partway? Possibly there is a mechanical failure and the springs are actually pushing it open the whole time and just the contact friction is holding it closed?
"Reset it and push it back on" sounds a lot more like a breaker than a switch.

I had to google "over-center" to make sure I understood you. Because I know how a disconnect operates, I could see how "over-center" is the descriptive name for the mechanism. I found this definition: "An overcenter linkage or device is used to provide a mechanical stop in a linkage and prevent any backdriving of the mechanism." This would prevent gravity from pulling the switch blades down. The real mystery is, "What is pulling the handle down, gravity or human hand?"

I agree with the other posters that the most likely problems are mechanical failure of the switch or mischief.

The solution would be locking in the "on" position in the case of mischief. You may have to drill a hole and then install tiewrap or padlock.

If GoldDigger's diagnoses holds true, then switch replacement is indicated.

 

[zog]

I see we are on the same page. No breaker has tripped or fuse blown. The safety switch handle will be in the halfway position. I reset it and pust it back on and it will work until who knows when. It makes no sense to me or anyone else I've talked to today. My problem is I have a owner who keeps calling me and I haven't got an anwser. Doesn't make me look very good.

I think we have some poor terms here, a safety switch can't "trip". Please post a photo of this switch.

 

[ryanpickett2003]

My Apologies, It is a fused disconnect and we have ruled out someone tampering with it. There is a security camera at the service. Thanks for the help.

 

[kwired]

If it is not being tampered with and is "falling" open on its own, there is a good chance it is going to fail sometime soon anyway. If it falls open that easily there can't be that much contact pressure and contact points will eventually burn out - unless maybe there is relatively small load on it, then that may buy some time.

 

[ptonsparky]

If it is not being tampered with and is "falling" open on its own, there is a good chance it is going to fail sometime soon anyway. If it falls open that easily there can't be that much contact pressure and contact points will eventually burn out - unless maybe there is relatively small load on it, then that may buy some time.

I have different take...it has failed already. Zog would repair it, most of us should just replace it.

 

[kwired]

I have different take...it has failed already. Zog would repair it, most of us should just replace it.

Yes, it has failed already, just has not failed to the point where it will not perform its function at all.

 

[Cow]

My Apologies, It is a fused disconnect and we have ruled out someone tampering with it. There is a security camera at the service. Thanks for the help.

Change the disconnect before your customer has any more unscheduled power outages.

 

[zog]

I have different take...it has failed already. Zog would repair it, most of us should just replace it.

If it is just a 400A LV switch it is not worth a repair, just replace it.

 

[Jraef]

Could be a Bolted Pressure (aka "Pringle") Switch, they can have Shut Trip or Under Voltage Trip coils installed in them and when activated, the handle will go to a center position. The same is true of the old ITE "Vacu-Break" switches. The trip coils are usually used in conjuntion with a GF relay or a power monitor relay. It could very well be that the entire system is doing EXACTLY what it was designed to do, prevent further damage to the equipment down stream because of a ground fault or a phase loss, surge or sag.

Generally, BP switches are used for higher amperages, but they do make them in 400A. As a general rule, a BPS will have a long lever handle on the front door, as opposed to a side mounted handle like on a slot machine. but without knowing what you have, that would be my first guess.

 

[zog]

That was my first thought too, wish the OP would provide some details

 

[kwired]

Could be a Bolted Pressure (aka "Pringle") Switch, they can have Shut Trip or Under Voltage Trip coils installed in them and when activated, the handle will go to a center position. The same is true of the old ITE "Vacu-Break" switches. The trip coils are usually used in conjuntion with a GF relay or a power monitor relay. It could very well be that the entire system is doing EXACTLY what it was designed to do, prevent further damage to the equipment down stream because of a ground fault or a phase loss, surge or sag.

Generally, BP switches are used for higher amperages, but they do make them in 400A. As a general rule, a BPS will have a long lever handle on the front door, as opposed to a side mounted handle like on a slot machine. but without knowing what you have, that would be my first guess.

But this is supposedly a fused switch and there has been no blown fuses, just an open switch.

 

[Jraef]

But this is supposedly a fused switch and there has been no blown fuses, just an open switch.

A BPS is often fused, making it a "fused switch", or like I said, the ITE / Siemens Vacu-Break switches with fuses are "fused disconnect switches" to the untrained eye, and both can be fitted with trip coils. If the OP would be so kind as to post a brand name and model, or even a picture, this can likely be cleared up quicker. If there is a Ground Fault relay somewhere connected to that trip coil, it would open the switch MUCH faster than it would take for the fuses to clear. That's actually the point of it. Same on a phase monitor relay; loss of a utility phase or low voltage, for even a second, may cause the relay to change state and trip the coil, which would move the handle to a center position. The original installer may have known there were supply problems there and used the BPS because it could be fitted with a trip coil, unlike a basic "one-armed-bandit" safety switch.