Pistol grip 2

[tulum]

I am installing some vacuum switchgear, and there is a little mix up in the pistol grip for the main breaker. We ordered the same grip as used in a previous job, which in the database said it had an interrupting current of 5A. However, when it got here it actually was only good for 3A. The VCB has a trip coil with a continuous current rating of 3A.

Is it alright to use a switch whos interrupting rating is equal to the continous trip coil rating? I usually buy a size up...

If not.. is it standard practice to use an interposing relay in the main trip circuit? Seems to me this would just be another piece of equipment that could malfunction between me and the trip coil?

 

[stevenal]

The breaker will usually use an auxiliary contact to interrupt the trip current.

 

[tulum]

Stevenal,

Come again? I don't know if were on the same page??

What I am talking about is tripping the breaker? Not the mains?

As per the manufactures drawings, my pistol grip will feed directly the trip coil of the breaker. This is the rating I am wondering about...

 

[BEPC13]

What he means is when you close the pistol switch to trip the breaker there will be 3A of current flowing through the switch. But typically there are 52a switches wired in series with the trip coil to interupt the tripping circuit. This ensures that if the breaker trips and the contact energizing the trip coil does not open you do not burn out the trip coil. Therefor these contacts will be the ones interupting the current not the switch itself.

 

[jbartos]

Comment: Normally, breakers have 86 lockout relays with pistol grips. Although other switching devices, e.g. control switch may come with the pistol grip.

 

[tulum]

Gotcha..


Thanks Stevenal and BEPC13...it is clear now...

Stevenal, I was not being crass, I merely did not understand. However, Reading the post back it looks like that even to me...

Thanks again...

Regards,
Tulum

 

[busbar]

To achieve certain DC-interrupting ratings with control switches, up to four series contacts on the switch assembly may be required. For example, see rating charts in

http://www.geindustrial.com/products/brochures/sb1.pdf

 

[jbartos]

Comment: The original posting does not indicate the switchgear control voltage. It can be AC or DC. Voltages can also be different, e.g. 120VDC, 250VDC, 120VAC, etc. It seems to me that the posting contact current ratings such as 3A were somehow obtained by intuition? or communications outside of this Forum? How strange.

 

[tulum]

jbartos,

It states in the original post that the contact current ratings were 3A. The voltage rating is 125vdc, but was not a concern for this question so was not mentioned.

I don't know these people, and I have never had contact with them outside this forum.

 

[jbartos]

Suggestion: Any contact current interrupting rating is meaningful when it is correlated to the contact circuit voltage. See for example a table "Interrupting Ratings" in the link posted by busbar. The reason why voltage is required is that the contact is actually energetically rated, i.e. energy=voltagexcurrentxtime, in VAseconds or Wattseconds in some instances.