I want to know if anybody has encountered this problem too. The problem that I have with other people's PVC conduit installations ( but not my own ) that are exposed to cold temperatures is that the PVC conduit detaches from box connectors and LBs and then permanenly shrinks 1 to 6 inches depending on the length of the conduit run and how cold the environment gets.
To make things worse, some of these broken conduit runs are shorter than the length at which NEC requires and expansion joint.
In outdoor installations only 1 end of the PVC conduit deteaches from the box connector or LB but in blast freezers both ends of even a short run of PVC conduit detaches from the box connectors.
I am thinking of several causes of this:
1. The extrusion process for the pipe somehow creates a memory effect that operates at cold temperatures rather than heat shrinking. Some of these conduits do not have the sun beating on them long enough to create heat shrinkage.
2. I am suspicious that the diameter of the conduit shrinks faster than the diameter of injection molded parts such as box connectors and LBs.
3. The grey PVC cement that is alleged to be optimal for electrical pipe somehow creates weak joints that pull apart easily after a few years. Even a small bump from a pedestrian can break a joint.
4. I have always used clear of purple primer plus all weather ( cold temperature ) solvent cement using the same technique as for pressurized water pipes. I have not had a joint break even though some of my installations were theoretically just a little longer than the length at which NEC requires an expansion joint an I did not install an expansion joint at the time because back in 1993 NEC did not have a criteria as to when an expansion joint was required. That my joints going back to 1987 have not broken and about 10 year old work by others that is broken points to some kind of workmanship problem or maybe a change in manufacturing parameters.
One reason why I always use all weather solvent cement is that most of my customers do not think about outdoor lighting until Daylight Savings Time expires. Even if a business owner is a genius, he closes his store at 6 p.m. and then hits the sack before sunset during the summer. There is also the issue of cash flow such that outdoor electrical work gets deferred until the cold half of the year. Yes, I have tied an electric heater to one of the rungs of the ladder to keep my hands warm. I have had only about 1 instance where a major lighting project was done during the springtime.
5. Come to think of it, I have to buy primer from a plumbing supply house or from the plumbing section of a combined electrical and plumbing supplier. What I have been told by strictly electrical supply houses is that they do not carry primer because other electricians do not use it.
6. In some dirty industrial situations, dirt would tend to jam expansion couplings even if one were installed.
7. Some electricians tighten conduit fasteners so tight that an expansion coupling would not work if installed.
8. In some industrial situations, dirt would tend to contaminate primer and solvent cement.
What is your take on this?
Mike Cole
To make things worse, some of these broken conduit runs are shorter than the length at which NEC requires and expansion joint.
In outdoor installations only 1 end of the PVC conduit deteaches from the box connector or LB but in blast freezers both ends of even a short run of PVC conduit detaches from the box connectors.
I am thinking of several causes of this:
1. The extrusion process for the pipe somehow creates a memory effect that operates at cold temperatures rather than heat shrinking. Some of these conduits do not have the sun beating on them long enough to create heat shrinkage.
2. I am suspicious that the diameter of the conduit shrinks faster than the diameter of injection molded parts such as box connectors and LBs.
3. The grey PVC cement that is alleged to be optimal for electrical pipe somehow creates weak joints that pull apart easily after a few years. Even a small bump from a pedestrian can break a joint.
4. I have always used clear of purple primer plus all weather ( cold temperature ) solvent cement using the same technique as for pressurized water pipes. I have not had a joint break even though some of my installations were theoretically just a little longer than the length at which NEC requires an expansion joint an I did not install an expansion joint at the time because back in 1993 NEC did not have a criteria as to when an expansion joint was required. That my joints going back to 1987 have not broken and about 10 year old work by others that is broken points to some kind of workmanship problem or maybe a change in manufacturing parameters.
One reason why I always use all weather solvent cement is that most of my customers do not think about outdoor lighting until Daylight Savings Time expires. Even if a business owner is a genius, he closes his store at 6 p.m. and then hits the sack before sunset during the summer. There is also the issue of cash flow such that outdoor electrical work gets deferred until the cold half of the year. Yes, I have tied an electric heater to one of the rungs of the ladder to keep my hands warm. I have had only about 1 instance where a major lighting project was done during the springtime.
5. Come to think of it, I have to buy primer from a plumbing supply house or from the plumbing section of a combined electrical and plumbing supplier. What I have been told by strictly electrical supply houses is that they do not carry primer because other electricians do not use it.
6. In some dirty industrial situations, dirt would tend to jam expansion couplings even if one were installed.
7. Some electricians tighten conduit fasteners so tight that an expansion coupling would not work if installed.
8. In some industrial situations, dirt would tend to contaminate primer and solvent cement.
What is your take on this?
Mike Cole
