PQexplorer
Member
Aprox. How long will a set of THHN/THWN (90?C) feeders last on a typical office building without any special environment, and housed in cable trays and other raceways?
10-15 years...
10-15 years...
Wiring useful life
- Thread starter PQexplorer
- Start date
- Status
bphgravity
Senior Member
- Location
- Florida
Re: Wiring useful life
The wiring systems of today should be able to last the life of the building if not exposed to conditions outside of what they are rated for. An exact number of years is really not possible to be determined. If the feeders are of sufficient age and/or showing signs or wear and deteriation, insulation testing can be performed to determine integrity. Age by itself is not a practicularly good indicator of conductor life.
The wiring systems of today should be able to last the life of the building if not exposed to conditions outside of what they are rated for. An exact number of years is really not possible to be determined. If the feeders are of sufficient age and/or showing signs or wear and deteriation, insulation testing can be performed to determine integrity. Age by itself is not a practicularly good indicator of conductor life.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
Re: Wiring useful life
I would say that THHN should last at least 100 years or more. I've worked on houses with knob and tube wiring that's 70-80 years old and still functioning. And that was with the highly inferior, rubber insulated RW or RHW insulation.
I would say that THHN should last at least 100 years or more. I've worked on houses with knob and tube wiring that's 70-80 years old and still functioning. And that was with the highly inferior, rubber insulated RW or RHW insulation.
Re: Wiring useful life
In light of this question I would like to know how some of you guys deal with older homes that were wired with the old BX type cable that had wire that had a braided fabric covering over a rubber coating on the wire. All too many times I have seen this wire drop all the insulation and rubber all the way back to the back of the box. If you dont disturb it, its OK, but if you go to change an outlet or a switch the insulation just disintegrates. Some electricians wont even work on a house with this kind of wiring.
In light of this question I would like to know how some of you guys deal with older homes that were wired with the old BX type cable that had wire that had a braided fabric covering over a rubber coating on the wire. All too many times I have seen this wire drop all the insulation and rubber all the way back to the back of the box. If you dont disturb it, its OK, but if you go to change an outlet or a switch the insulation just disintegrates. Some electricians wont even work on a house with this kind of wiring.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
Re: Wiring useful life
This is a pretty common practice around here since many newer lighting fixtures now contain a note on them about only installing them with conductors rated for 75 or 90 degrees.
We work in a lot of older homes with BX that's 50-60 years old. The problem with crumbling insulation is usually at the light fixture outlets where years of heat have dried out the old RH, rubber conductors. Many times if the home has an attic we remove the old cable from the ceiling box and cut back about a foot or so from the bad end. This will expose conductors that haven't been affected by the heat. We will then install a junction box and put in a new piece of cable to the existing fixture outlet.
This is a pretty common practice around here since many newer lighting fixtures now contain a note on them about only installing them with conductors rated for 75 or 90 degrees.
hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
- Occupation
- EC
Re: Wiring useful life
In light of this question I would like to know how some of you guys deal with older homes that were wired with the old BX type cable that had wire that had a braided fabric covering over a rubber coating on the wire. All too many times I have seen this wire drop all the insulation and rubber all the way back to the back of the box. If you dont disturb it, its OK, but if you go to change an outlet or a switch the insulation just disintegrates.
Yes and this happens at all box locations not just those exposed to high temperatures at fixtures. The rubber gets hard and becomes brittle with age. My experience has been that this seems to be limited to certain BX cable manufactured during a short period of time.
I've found that BX in older buildings, say dating back to the early 40's and before is fine even today. Cable installed in buildings around 1955 commonly has this problem. I know because my house is one. Cable manufactured a few years later until the RW was replaced by TW seems to be fine.
-Hal
In light of this question I would like to know how some of you guys deal with older homes that were wired with the old BX type cable that had wire that had a braided fabric covering over a rubber coating on the wire. All too many times I have seen this wire drop all the insulation and rubber all the way back to the back of the box. If you dont disturb it, its OK, but if you go to change an outlet or a switch the insulation just disintegrates.
Yes and this happens at all box locations not just those exposed to high temperatures at fixtures. The rubber gets hard and becomes brittle with age. My experience has been that this seems to be limited to certain BX cable manufactured during a short period of time.
I've found that BX in older buildings, say dating back to the early 40's and before is fine even today. Cable installed in buildings around 1955 commonly has this problem. I know because my house is one. Cable manufactured a few years later until the RW was replaced by TW seems to be fine.
-Hal
- Status