Hendrix
Senior Member
- Location
- New England
What danger does URD pose if it enters a building?
URD
- Thread starter Hendrix
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A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
It doesn't have a flame retardant insulation unless it is of the 8000 variety.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If I understand your question correctly, I see two factors:
1. If the Underground Residential Distribution (service?) wire enters a building, the fact that it is not well protected against overload short of a bolted fault can make it a fire hazard. Once the service wiring has reached the service disconnect, which must contain OCPD, this hazard is no longer present.
2. If you use the same wire type inside a building after the service disconnect (if allowed at all for that wire type) it will typically not contain both a grounded conductor and a grounding conductor and so will not serve the purpose.
3. And what he said.....
A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
Gold....what is that?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
I was thinking of a rubbed or damaged insulation type fault within the cable. It could be high enough resistance (because of small surface area) that it could carry a substantial overload and generate lots of local heat, but not necessarily enough to trip protection on the POCO side.
Of course more common would be a dead short which because of the length of the wiring involved would still not trip POCO protection.
Good point.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The main issue is that the insulation does not have a vertical flame rating. Much of what people call URD is really dual rated conductors that are thhw/thhn. This would be legit in a house in a raceway. The true URD is not acceptable in the NEC as far as I know.
- Location
- Massachusetts
A fine point but the service disconnect does not have to contain the OCPD. The OCPD can be contained in the enclosure with the service disconnect or be located immediately adjacent too it.
The only scenario I can see this being the case is when using a service rated transfer switch as the service disconect that does not have an internal OCPD.
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