Electrical terminal clearances

[Sparkyonline]

I have received some heating elements that have been constructed out of the norm for this vendor.

The concern at this point is that proper clearances have not been maintained phase to phase.

575V 3Ph

Anyone have any information or a source that will outline these clearances....NEMA website not a lot of help.

Thanks

 

[advidana]

Try contacting UL or a testing outfit. That what these guys do for living.

 

[TMD]

Spacing between bare live parts depends on who is doing the certifying. Different agencies have different requirements. And there are differences depending on teh equipment; that is, switchgear is different from motors which are different from junction boxes, etc. First thing to do is determine who's rules you need to comply with.

 

[Sparkyonline]

equipment manufactured in US.....end user in Canada....


basically is a NEMA requirement.........

UL standards also apply...

 

[TMD]

I'm in Canada, so we sometimes deal with CSA. More often marine authorities, like ABS, DNV, etc. Anyway, depending on the equipment, CSA C22.2 #14, Industrial Control Equipment, may be appropriate. Also look at C22.2 #31, Switchgear Assemblies. There may be others. You really need to read the standards to interpret the spacings. Look on

http://www.csa-international.org.

I'm sure there are UL standards that are more or less equivalent to CSAs. There's probably a standard for heaters that will give you the answer you need.

 

[PWR]

NEMA Standard AB-1 for molded case breakers lists 1 inch clearance through air for potentials of 301 to 600VAC.

Powell Electrical Manufacturing Technical Brief PTB #59 mentions that ANSI switchgear standards do not list such clearances but goes onto say they (Powell) use 1 inch between bare conductors up to 635V.

 

[gettmank]

The requirements in UL 499, Standard for Electric Heating Appliances, is for 3/8 inch through air spacing and 1/2 inch over surface spacing between field wiring terminals. The CSA requirement is probably roughly equivalent. This requirement comes from table 25.1.

For the voltage referenced, this is a typical requirement given the considerations concerning potential for loose strands from the supply wiring and potential for overly long stripped insulation during the installation, creating the potential for bridging the two circuits.

In the IEC, assuming an overvoltage withstand rating of 6 kV, based on the supply voltage and the likely installation category, in standard 664-1, Insulation Coordination, the required through-air spacing [clearance] would be 5.5 mm and the over-surface [creepage distance] would be 9 or 10 mm depending on the material. There may be other considerations but your posting does not provide any other details.

 

[Sparkyonline]

Thanx guys....

good info...

received response from manufacturer via vendor today stating that their UL approved clearance for these elements 6KW @ 575V is a minimum of 1/4" phase to phase......

Thanx for your time.

 

[busbar]

(99 NEC) Table 384-36. Minimum Spacings… would probably apply, and could be reduced by overpotential type testing and labeling through a standard like UL508, at the discretion of the AHJ.