By Grant Laidlaw
Many people ask for assistance in the understanding of theoretical and practical aspects of the industry. I will endeavour to enlighten. We are going back to basics as I have questions coming in that indicate that the basic understanding and skills necessary to work in our industry are simply not in place.
“Hello Mr Grant. Can you please give me some help? We work with PVC conduit in our installations. We would like some advice on using, joining and bending. Thank you for all the good advice, Sam.
Thank you for your question, Sam. The following represents good practice when working with PVC conduit. PVC conduit with a wide range of accessories is available, allowing for fast and simple installations.
PVC conduit is used in the same way as metal conduit but should be protected from mechanical damage and high temperatures. PVC is resistant to most acids, alkalides and oils, does not attract rodents and can be buried in concrete, lime and plaster without harmful effects. The material is light and therefore easy to transport. Cutting is quick and simple using a PVC tube cutter. Bending: Sam, circular conduit not exceeding 25 mm in diameter can be bent cold using the correct size bending spring.
Unlike refrigerant tubing, where the spring bender is used on the outside surface of the tube, the PVC conduit spring is inserted into the tube. The springs have an eye on one end to which a cord could be attached if necessary. This will help remove the spring if the spring gets stuck in the conduit. The tapered end is for easy insertion into the conduit.
With the spring inserted into the tube, the bend can be made by hand or by using a hickey. Approximately twice the angle required should be bent and then the conduit allowed to return to the correct angle.
Thus, for a 90° bend it should first be bent through 180° and allowed to return to 90°. Do not force the tube to return with the spring inserted. Removal of the spring can be made easy by gently twisting in an anti-clockwise direction.
Sam, when using PVC conduit, the following points should be remembered:
- Saddle the conduit as soon as possible after bending.
- Care should be taken when using glue so as not to apply too much. Excessive glue may form a restriction.
- Insufficient glue will not make a watertight joint.
- PVC expands at a rate of approximately five times more than steel. Where necessary, expansion joints can be used. Up to 6mm per 4m length expansion can be experienced.
- For every 8m of straight run, an expansion joint should be used to prevent the tube from bending out of place on your nice straight run. Use silicon grease in the one side of the joint to facilitate movement and maintain a seal.
Sam, the following is a diagram of an expansion joint:
- Place a draw wire into the conduit as work progresses.
- In cold weather, gentle heat can be applied prior to forming bends. Rubbing with hands is often sufficient.
- Conduit should be saddled at ± one-metre intervals.
- To ease conductors through, a light smear of liquid paraffin or French chalk can be used.
- Bends should have a minimum radius of six times the inside diameter of the conduit.
- Correct spring bender size should be used.
- Care should be taken when using PVC conduit for light suspension due to the heat generated by some fittings.
Light and heavy-duty conduit is available in 16mm, 20mm, 25mm, 32mm, 38mm, and 50mm as well as flexible PVC conduit which is also available in multiple sizes.
Sam, your planning and layout is very important, and the following points should be considered prior to commencement of work:
- Consider gas, water and electrical lines
- Make sure the customer’s requirements have been met
- Make allowances for possible extensions
- Routing should be in accordance with codes of practice
- Mechanical protection may be required
When marking out, the following procedures should be followed:
- The position of all components should be determined and clearly marked
- Individual conduit runs should be marked out using a plumb line and a spirit level
- Accuracy is very important
High standards can be achieved by:
- Thorough planning
- Attention to detail
- Constant practice
- Pride in your workmanship
Thanks for your question, Sam, and I hope that this helps you with your work with conduit.