Breaker bypass switches

[jnims]

In my office, we have been discussing the necessity for using vacuumn bottles on breaker bypass switches at voltages above 69kV. Traditionally, gang-operated switches with arcing horns or whips are used (not vacuumn interupters) since the voltage accross the parting contacts is small. However, there is a statement on OSHA regulation 1910.269 (l)(10)

"Opening circuits under load." Devices used to open circuits under load conditions shall be designed to interrupt the current involved.

Our concern is does this statement apply to breaker bypass switches. If so, arcing horns and whips have very limited interupting capabilities and a vacuumn interupter is required. Obviously, the traditional way has been used sucessfully for many years. Several switch manufacturers have recommended using the vacuumn interupters over 69 kV to be conservative. While they have an interest in selling a higher priced product, they also must maintain some integrity.

So will the arcing horns or whips stand up to OSHA scrutiny or not?

 

[stevenal]

Please see my answer in the utility usenet group. An additional comment:
The requirement, as quoted, does not require switch to be able to open the available load current, but "the current involved". The current involved, parallel current through the switch, is easily broken as you have said.

 

[jbartos]

Suggestions:
1. OSHA refers to devices/iterrupters that are designed to interrupt the load current.
2. The bypass switch would have to open first and then the breaker that would then interrupt the load current or the upstream circuit breaker or adjacent circuit breakers would have to operate first before the bypass switch is opened. This would meet the OSHA safety requirements.

 

[busbar]

jnims, you could try posting this question at

http://www.powerlineman.com/safety_meeting/Safety_Discussion.htm

David Wallis, a senior electrical engineer at OSHA, (who was the primary author of 1910.269) gives informal interpretations of those rules, primarily to a readership of linemen. He usually posts responses about once a week.

 

[busbar]

David Wallis at OSHA addressed the issue on 19 Sep. at:

http://www.powerlineman.com/safety_meeting/discussion/0000029f.htm