Maximum Temperature Rise for Fused Disconnect

[haze10]

We started doing infrared testing of our Allen Bradley 2100 MCC buckets. There appears to be common hot spots where fused disconnect switches are employed. The hot spots are typically where the disconnect blade is hinged, where the blade meets its corresponding stab, and at the line side of the fuse clips. Ambient temperature is around 80F maximum. Temp rise on the hot spots can be a relatively low 15C to a high of 70C. My question is at what temperature rise do we need to replace the switch. I am seeing literature that says max rise should be limited to 30C or 50C. Does anyone have a threshold that they recommend.

Also, is it recommended to apply a conductive grease to the blades or fuse ends such as Penetrox, or MG Chemicals Carbon Grease?

Thanks,
gary

 

[waross]

I would hesitate to use Penetrox on moving parts.
Penetrox is not a lubricant, it is a joint compound.
From the Penetrox data sheet:

Non-Petroleum Base Vehicle With Zinc Particles Suspended

The zinc particles help penetrate the ubiquitous oxide film on aluminum, but may lead to accelerated wear on switch blades.
For an application where the switch is seldom operated I may use Penetrox.
For an operation where the switch is used often, such as for saw sharpening or changing or tool changing I would look for another product rather than chance accelerated wear of the switch blades.
For frequently operated switches I would look for a graphite based automotive lubricant.

 

[Compositepro]

In addition, the zinc particles are for corrosion protection, not for conducting large current. Particles act as spacers between two flat surfaces. You certainly do not want to use something with carbon.

 

[haze10]

Penetrox was a poor example. I would go more for this Thomas and Betts product which looks more appropriate:
"The CP8-TB Kopr-Shield Joint Compound (8 oz) from Thomas and Betts is the copper colloidal surface treatment that protects, lubricates, and enhances conductivity between connections. It is an ideal solution for reliable connections in electrical and raceway installations. This unique blend of pure, polished colloidal copper, rust and corrosion inhibitors is used for battery lugs and cables, raceways, fuse clips, contacts, drum switches and slip rings."

What I really need is a recommendation on max temperature rise, any comments about that?

 

[waross]

Most of the switches in an MCC should be fine. Clean and lubricate any outliers.
Once those are taken care of, you can lubricate all switches.
By the way, don't forget the influence of current.
Lightly loaded switches will run much cooler than switches loaded to their rating.
Don't forget I²R