Tom Maragnano
New member
I have been unable to find in NEC,NFPA 70B or Stalcup's a requirement for periodic torque on switch gear for a facility. Is there a rule of thumb or did I completely miss it?
periodic torque of switch gear
- Thread starter Tom Maragnano
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weressl
Esteemed Member
as Hamlet asks: to Torque or not to Torque?
as Hamlet asks: to Torque or not to Torque?
That seems to be the industry consensus from the maintenance side, however the equipment manufacturing side seems to differ.
As the result of an incident it was discovered that the factory torque-check marks over some Bellville washers were improperly applied, eg. the connections were never torqued. The factory insisted that after shipment and before service ALL connections should be re-torqued.
If a self-adjusting fastening method is used, such as the Bellville washers, nor re-torquing should be necessary unless the connection was subjected to severe vibrations. Such vibrations would need to exceed the most severe earthquake since the the washers are tested for several G's. In other words, either we are using/specifying fasteners that do not meet their intent and specifications or we are using manufacturers who can not be relied upon to manufacture equipment properly. Both would be irresponsible engineering, if not outright silly.
In short, IMO, the manufacturers of equipment require retorquing as a CYA.
GM published a paper showing that retorquing Bellville washers will actually result in defeating it's function and can result in developing hot-spot connections.
Torque marking of self-compensating connections should indicate that they require no further actions. Other connections should be properly torqued AND may be checked for the same torque value at periodic maintenance intervals. Some people advocate initial torquing to the minimum required and check-torquing later to a higher. Sounds like a sensible approach, but I have seen no published data to prove that it actually works.
as Hamlet asks: to Torque or not to Torque?
That seems to be the industry consensus from the maintenance side, however the equipment manufacturing side seems to differ.
As the result of an incident it was discovered that the factory torque-check marks over some Bellville washers were improperly applied, eg. the connections were never torqued. The factory insisted that after shipment and before service ALL connections should be re-torqued.
If a self-adjusting fastening method is used, such as the Bellville washers, nor re-torquing should be necessary unless the connection was subjected to severe vibrations. Such vibrations would need to exceed the most severe earthquake since the the washers are tested for several G's. In other words, either we are using/specifying fasteners that do not meet their intent and specifications or we are using manufacturers who can not be relied upon to manufacture equipment properly. Both would be irresponsible engineering, if not outright silly.
In short, IMO, the manufacturers of equipment require retorquing as a CYA.
GM published a paper showing that retorquing Bellville washers will actually result in defeating it's function and can result in developing hot-spot connections.
Torque marking of self-compensating connections should indicate that they require no further actions. Other connections should be properly torqued AND may be checked for the same torque value at periodic maintenance intervals. Some people advocate initial torquing to the minimum required and check-torquing later to a higher. Sounds like a sensible approach, but I have seen no published data to prove that it actually works.
zog
Senior Member
- Location
- Charlotte, NC
Well I just realized my 70B grew legs but the ANSI/NETA standard is based on it and I believe says the same thing.
Inspect bolted electrical connections for high resistance using one of the following methods:
1. Use of a low-resistance ohmmeter in accordance with Section 7.1.2.
2. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench
method in accordance with manufacturer?s published data or Table 100.12.
3. Perform a thermographic survey in accordance with Section 9.
The only time I would recommend using a torqe wrench (Besides installtion and aceptance tests or course) would be after a bolted fault or other similar event that may have loosened the connections.
IR scanning is not very effective either because it relies on line of sight which is not easy in most switchgear configurations, the bus sections are not easily accessable and IR scanning needs to be done under as full load as possible so you have some serious safety concerns there.
So using a microhmeter is the best method, we do this on every switchgear maintenence job and do find loose connection fairly often.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
This manufacturer wants re-tightening:
zog
Senior Member
- Location
- Charlotte, NC
A sticker installed in the 70's is a far cry from a standard. But if they insist use the right torque values.
weressl
Esteemed Member
This manufacturer wants re-tightening:
Yep, Cover Your Assets.
Don't you just LOVE the 4 different notices and warnings? It does not yet include the labels, tags and warnings to be placed by the installer and the user. Talk about ADD?!
See page 29 of Connector Theory and Application, A Guide to Connection Design and Specification, this article was posted by Smart$ a few years back.
Roger
- Location
- New Jersey
- Occupation
- Journeyman Electrician
zog
Senior Member
- Location
- Charlotte, NC
Yep, Cover Your Assets.
Don't you just LOVE the 4 different notices and warnings? It does not yet include the labels, tags and warnings to be placed by the installer and the user. Talk about ADD?!
Yet no arc flash label, the one that matters is missing
zog
Senior Member
- Location
- Charlotte, NC
I dunno, looks old, I don't work with anything that small so am not sure what it is.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
The practice I like is to torque at installation, then using a sharpie or similar put a line that indicates alignment between the nut and bolt. Then all that is necessary is a visual inspection to verify that the nut has not moved. You can do the visual inspection just before you shoot the IR camera.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
zog
Senior Member
- Location
- Charlotte, NC
New AC unit sitting on the floor waiting to be installed. Photo is from 2010.
And that has what to do with the OP about switchgear? Your sign is refering to wires and terminals, not switchgear bus connections.
zog
Senior Member
- Location
- Charlotte, NC
We do the same, each one of our techs is assigned a different color sharpie (We are hiring and pink is available) we use this method for all breakers and switchgear, that during final inspection not only can we visually verify all hardware is tight, we know who tightened it.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
zog
Senior Member
- Location
- Charlotte, NC
What do you mean switchgear could mean the enclosure? Are you suggesting he is asking about torque specs for the covers or something? I'll bet you a bumper sticker he is asking about the bus connections.
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