Siemens Sentron Breaker Trips when Energized

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I have a 150 amp Siemens Sentron Breaker. Its in a power and control panel for a large pump. The panel door has a rotary handle disconnect that operates the breaker. When you attempt to operate this from the open position to the close position, the breaker powers up then trips. I took the disconnect extension handle and bracket off and operated the breaker a few times, it works perfect. But when I assembled everything it would close then trip open. If you do it a few times it you can make it work.

The problem is I have a 480 volt to 120 volt transformer that blows fuses on the primary side every time the breaker trips or wont stay closed. Its a 2000 va transformer. I looked at sizing up the fuses but I according to 450.3(b) I am stuck with ten amp fuses. The fuses currently in are Bussman LP-CC-10.

Has anyone run into this situation before? The best thing to do would be to get the breaker to close and stay closed. I spent about two hours adjusting the handle and bracket and it still would operate properly.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have a 150 amp Siemens Sentron Breaker. Its in a power and control panel for a large pump. The panel door has a rotary handle disconnect that operates the breaker. When you attempt to operate this from the open position to the close position, the breaker powers up then trips. I took the disconnect extension handle and bracket off and operated the breaker a few times, it works perfect. But when I assembled everything it would close then trip open. If you do it a few times it you can make it work.

The problem is I have a 480 volt to 120 volt transformer that blows fuses on the primary side every time the breaker trips or wont stay closed. Its a 2000 va transformer. I looked at sizing up the fuses but I according to 450.3(b) I am stuck with ten amp fuses. The fuses currently in are Bussman LP-CC-10.

Has anyone run into this situation before? The best thing to do would be to get the breaker to close and stay closed. I spent about two hours adjusting the handle and bracket and it still would operate properly.

have you considered using FNQR fuses instead? They are made to handle xfmr inrush better and will fit in the same fuse holders.

as for the MCCB tripping, when it trips is there a load on it? is there any kind of shunt trip by any chance?

It seems unlikely that a properly configured handle and operator would cause the thing to trip since there should be no pressure on the handle at all if the mechanism is correct.

Having said this, I have on occasion run into people who did not have the right parts and cobbled something up that looks like it should work. have you verified that the correct operator and handle and fasteners have been used? has it ever worked for any length of time?

One other thing, if it is old enough, there was a major problem with DG series breakers a few years ago to the point that Siemens was not even shipping them for the better part of a year. You might want to check with Siemens and see if it needs to be recalled.
 

iwire

Moderator
Staff member
Location
Massachusetts
This may sound basic but is there any chance something is hitting the trip button when the door is closed or any mechanism hardware installed incorrectly allowing the button to be hit?

ny8nbt-siemens-hfd63b150-image_1.jpg
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The trip mechanism in a breaker is not tied to the handle operation of the breaker. If it is tripping, something is MAKING it trip.

Have you checked the mag trip settings? Are they too low to handle the inrush of the transformer perhaps? Also, as mentioned, make sure there isn't a Shut Trip or an Under Voltage Release coil in that breaker. In fact, a UVR in that breaker, if tied to the 120V circuit, would trip if the transformer fuses are blowing. So what you might be seeing is that the transformer fuses blow first, which then trips the breaker because it has a UVR.

LP-CC fuses, although technically "time delay" are also "fast acting", intended for protecting sensitive devices like electronics. Bussman does not recommend using LP-CC fuses as transformer primary protection. FNQ-R is the correct midget fuse to use for that.
 

GoldDigger

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Location
Placerville, CA, USA
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Retired PV System Designer
Any idea why the inrush could be different between handle and lever operation, or do you think that is a red herring?
Something weird like closing at a different (random?) phase angle
 

Jraef

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Staff member
Location
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Electrical Engineer
Any idea why the inrush could be different between handle and lever operation, or do you think that is a red herring?
Something weird like closing at a different (random?) phase angle

How about this SWAG?

In order for him to use the breaker toggle handle directly, the door must already be open. When the door is closed and he is using the exterior handle, the transformer is warmer and has lower resistance, so the inrush is slightly higher.
 
I will definitely ordering FNQR fuses first thing tomorrow.

It works 100% of the time with the mechanism off, so I dont think it is the load. I am definitely leaning towards iwire's suggestion. Its usually the simplest thing.

I've checked for a shunt trip and I didnt see one. The breaker looks exactly like the image iwire posted.

Thanks for the posts.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
If you end up wanting to replace that breaker, I can tell you that you probably won't want to call your supply house and tell them you want a(I'm guessing the part # here)FXD63B150, or they'll slam you on the price. But, if you can order a 150A main breaker kit for a Siemens panelboard that comes with this breaker in it, it'll be considerably cheaper, usually. I've done it with Siemens 200's and 400's, I haven't tried buying a 150 yet.

Or a breaker surplus company would be another cheaper alternative for a new breaker.
 
If you end up wanting to replace that breaker, I can tell you that you probably won't want to call your supply house and tell them you want a(I'm guessing the part # here)FXD63B150, or they'll slam you on the price. But, if you can order a 150A main breaker kit for a Siemens panelboard that comes with this breaker in it, it'll be considerably cheaper, usually. I've done it with Siemens 200's and 400's, I haven't tried buying a 150 yet.

Or a breaker surplus company would be another cheaper alternative for a new breaker.


Thank you for the advice. But if I do end up replacing it, I will probably try to find comparable Square D breaker.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Thank you for the advice. But if I do end up replacing it, I will probably try to find comparable Square D breaker.

If you change to a Square D breaker, your linkage won't work. There's nothing wrong with the Siemens Sentron breakers, there must be a million out in the field. I see them all over, some of them I've even installed.;)
 

Tony S

Senior Member
With the door closed and the breaker in the on position is there any play in the handle? If there isn’t the door mechanism could be holding the breaker just off the fully latched position.

I’ve had this happen with various makes of breaker, all due to slight misalignment.

One episode had us chasing faults that weren’t there. The breaker seemed to close OK but when the contactor closed the vibration tripped the breaker as it wasn’t fully latched. That had us testing the motor, cables, etc. anything but look at the breaker.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
With the door closed and the breaker in the on position is there any play in the handle? If there isn’t the door mechanism could be holding the breaker just off the fully latched position.

I’ve had this happen with various makes of breaker, all due to slight misalignment.

One episode had us chasing faults that weren’t there. The breaker seemed to close OK but when the contactor closed the vibration tripped the breaker as it wasn’t fully latched. That had us testing the motor, cables, etc. anything but look at the breaker.
Well, technically that's not SUPPOSEDLY to be possible, but we all know better in the real world. :happyyes:
 
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