Minimum size of MV Cable used in Industry

Status
Not open for further replies.

mull982

Senior Member
I was curious if there is a minimum size Medium Voltage cable that is typically used in industry as the minimum size even though the calculated load may allow a smaller size cable?

In other words is there a standard practice that MV cables typically aren't used smaller then say a #2 etc... regardless of load? I don't ever recall seeing a #6 or #8 MV cable in any of the installations I have see (maybe the load required larger cable or maybe b/c its good practice to pull a minimum size)?

With MV cables is it typical to use the MV-90 or MV-105 type cable?

Thanks
 

mkgrady

Senior Member
Location
Massachusetts
I was curious if there is a minimum size Medium Voltage cable that is typically used in industry as the minimum size even though the calculated load may allow a smaller size cable?

In other words is there a standard practice that MV cables typically aren't used smaller then say a #2 etc... regardless of load? I don't ever recall seeing a #6 or #8 MV cable in any of the installations I have see (maybe the load required larger cable or maybe b/c its good practice to pull a minimum size)?

With MV cables is it typical to use the MV-90 or MV-105 type cable?

Thanks

I have never seen an mv cable smaller tha #6 and usually not smaller than #2. I suspect it is because the smaller sizes are so uncommon that nobody buys them so they are not worth manufacturing. Another guess is that they would be fragile compared to larger sizes
 

paulengr

Senior Member
NEC has a cutoff of #2 somewhere. Only time I see smaller is frequently you may see small bare wires connecting lightning arresters on overhead switchgear such as #4. The small size makes it a fuse. It will vaporize during a direct lightning strike or if the lightning arrester fails by shorting to ground. There is design info for this but its mostly a home grown thing, not following a Code or standard. Smaller unshielded transformer hookup wire often rated 5/15 kV rated on insulators with fiber board channel tied in place as spacers is often used inside enclosures for PT and CPT leads, such as leads from the load side of very small 1E or 2E rated fuses to a 1 kva 35 kv:120 V PT. This is a place where very good design/testing practices and closely monitored quality control is critical.
 

wsbeih

Member
Location
USA
I was curious if there is a minimum size Medium Voltage cable that is typically used in industry as the minimum size even though the calculated load may allow a smaller size cable?

In other words is there a standard practice that MV cables typically aren't used smaller then say a #2 etc... regardless of load? I don't ever recall seeing a #6 or #8 MV cable in any of the installations I have see (maybe the load required larger cable or maybe b/c its good practice to pull a minimum size)?

With MV cables is it typical to use the MV-90 or MV-105 type cable?

Thanks

Practically and due to short circuit concerns, #2AWG and larger is what I'm used to see. I typically specify MV-105 in order to take advantage of higher ampacity as I de-rate the cable for various factors including Tray size/fill/ampacity rules (392.80), ductbank heating, termination limitations.
 

topgone

Senior Member
Practically and due to short circuit concerns, #2AWG and larger is what I'm used to see. I typically specify MV-105 in order to take advantage of higher ampacity as I de-rate the cable for various factors including Tray size/fill/ampacity rules (392.80), ductbank heating, termination limitations.
Correct! Also, you can't buy what's not available, you know?
 
Status
Not open for further replies.
Top