Mike Dolt Enterprises
Mike Dolt Enterprises
User: wil-design, Location: Florida
Asked on: Saturday, December 14, 2024 at 8:25 am EST
Answered on: Thursday, March 6, 2025 at 6:19 am EST
Question: We have a concrete contractor requiring that our piping prior to a concrete pour not be strapped directly to rebar via usual methods consisting of use of wrapped twisted tie wire.To comply, we are suspending the conduit and fittings away from the rebar using tie wiring in different directions to keep the encased conduit and fittings including Rob Roy stub ups "floating" thus keeping them from physically touching the rebar ( even if it is just a fraction of an inch )-- no minimum gap distance is specified. The job site is at a industrial location.This verbal requirement by the contractor includes installation of RobRoy ( Plasti-Bond PVC Coated Aluminum ) conduit and PVC plastic conduit in smaller sizes such as 1 inch, 4 inch, and 2 inch. There is no written specification that he can specify in his prints or that we can find in our documentation. Voltages are 480 Volts maximum.Is this a common industry practice by a concrete contractor imposed on our trade for industrial installations ( paper mills, water reclamation plants, powerhouses, etc.?I do not have many contacts in my industrial electrical trade nor structural engineering trades, etc. We are trying to comply with the contractors wishes and I do not have the contacts or resources for professional advice.I have thought about contacting the manufacturer of the Rob Roy conduit to find out if they show that contact of their coated conduit with standard steel rebar resists corrosion and weakening of the structural rebar which is the reason we have been given by the contractor. The same for manufacturer of the PVC conduit.One workaround is to use tie wire fashioned to create a small gap between the conduit and the rebar since obviously tie wie contact with rebar is Ok. The concrete contractor has rejected this idea.The concrete contractor has also rejected the use of thin cut 1/4" or 1/2" slices of scrap PVC to be strapped via tie wire between the piping and rebar. I do see his side of the issue that if the PVC is allowed to be strapped parallel to the rebar for more than a few inches that unequal rates of expansion and contraction of the concrete and rebar vs. the hollow plastic and plastic coated piping could cause a crush zone and allow the rebar to shift and comprimize its structural purpose.Keeping the electrical piping away from parallel lengths of rebar via some minimum distance such as using sections of cut PVC spacers cut to say, half an inch in spacing, to be sufficient to keep the piping lengths from getting too close as it distorts and flexes before permanently being encased after the pour.Their requirement seems both rare and unreasonable for our electrical installation but would in fact be reasonable if we, for example, improperly used bare metal piping, fittings, etc. contacting rebar for this encased in concrete application I will admit. The increased labor and manpower costs are a part of compliance which we are doing. We are looking for alternative solutions that can be shown / proven will not compromise the structure.Any advice in this matter would be greatly appreciated.Bryan
Bryan, you've got a challenging situation. Let's break down the contractor's concerns, the validity of their requirement, and potential solutions.
Understanding the Contractor's Concerns
The contractor's primary concern seems to be preventing corrosion of the rebar and/or weakening of the concrete due to interaction with the electrical conduit. Here's what might be underlying their thinking:
Galvanic Corrosion (Unlikely with your materials, but understandable concern)
The contractor might be concerned about galvanic corrosion. This occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (like the moisture in concrete). While Rob Roy is PVC coated aluminum, and PVC conduit is non-metallic, the potential for some point of contact allowing the conduit to ground fault to nearby steel rebar might lead to this concern. In reality this is likely not a reason for his concern but it is listed for consideration.
Stress Points/Differential Expansion
As you correctly identify, differential expansion and contraction between the conduit (especially plastic or plastic-coated) and the concrete/rebar can create stress points within the concrete. This could, in theory, lead to cracking or weakening of the concrete around the conduit. This would be more of a concern with larger diameter conduit runs placed tightly parallel to rebar, which you already pointed out. This is probably his leading concern.
Bonding Issues
Some contractors believe that any foreign object directly touching the rebar might interfere with the concrete's ability to properly bond to the rebar. This is less likely to be a significant issue but is another possible (though unfounded) concern.
Is the Contractor's Requirement Common/Reasonable? Generally Uncommon
Directly strapping conduit to rebar with tie wire is a very common practice in the electrical industry when embedding conduit in concrete. I've worked on many similar projects (wastewater treatment plants, power generation, etc.) and never encountered this restriction.
Potentially Reasonable (with caveats)
Completely unreasonable to apply such a restriction uniformly across all conduit regardless of size, material, and placement. Bare metal conduit: If you were using uncoated metal conduit, there would be a more justifiable concern, though even then, it's often managed through proper grounding and bonding practices. Large diameter, high density runs: As you mentioned, large runs of conduit tightly parallel to rebar could theoretically create stress points due to differential expansion/contraction.
What about Code Compliance? NEC is Silent
The NEC (National Electrical Code) doesn't explicitly prohibit or require spacing of embedded conduit from rebar. It focuses on proper installation methods, conduit type suitability for the environment, and grounding/bonding.
Recommended Actions and Solutions
Communication is Key
Politely Challenge the Contractor
Request the contractor to provide written documentation (specs, engineering justification, etc.) that supports their requirement. Ask specifically what problem they are trying to prevent. Framing it as "we want to ensure we understand the underlying issue so we can find the best solution" can be helpful.
Explain Standard Practices
Explain that direct strapping is the standard industry practice and ask why their experience necessitates a deviation from that standard. Emphasize the increased labor and time costs associated with their requirement.
Document Everything
Keep a record of all communication with the contractor regarding this issue, including dates, times, and specific points discussed.2.
Seek Expert Opinion (and Documentation)
Conduit Manufacturer (Excellent Idea)
Contact Rob Roy and the PVC conduit manufacturer. Ask them for their official recommendations for embedding their conduit in concrete, specifically regarding contact with rebar. Request any technical data sheets or documentation that address this. This is your strongest potential argument.
Structural Engineer (If Possible)
If the stakes are high enough (large project, critical infrastructure), consider consulting with a structural engineer. They can provide a professional opinion on the potential impact of embedded conduit on the concrete structure. This can be expensive but can provide solid documentation.
Industry Associations (e.g., NECA)
Contact your local NECA chapter (if you're a member) or another relevant electrical industry association. They may have experience with similar situations and be able to offer guidance.3.
Present Alternative Solutions (Negotiate)
Instead of a complete, costly floating system, propose these alternatives:
Controlled Spacing
The cut PVC spacers are a good idea, but consider a more robust approach. Use manufactured plastic spacers designed for this purpose. There are plastic "chairs" and supports that create a consistent, small gap between the conduit and the rebar. Present these as a compromise that addresses his expansion/contraction concerns while still allowing for efficient installation. Some are specifically designed to clip onto the rebar.
Strategic Placement
Can you route conduit in a way that minimizes contact with rebar? Perhaps running it along the forms when possible?
Limited Floating Zones
Can you agree to only "float" specific areas where the conduit runs parallel to and in close proximity to multiple runs of rebar? This limits the increased labor costs to the areas where the contractor's concern might be most valid.
Gap with Tie Wire
As you mentioned, use tie wire fashioned to create a small gap between the conduit and the rebar since obviously tie wire contact with rebar is Ok. Even a small gap of 1/8" or 1/4" would address differential expansion concerns.
"Foam Tape"
Consider heavy-duty foam tape. It can be applied to the conduit (particularly at contact points), and compressed tie-wire holding the assembly together.4.
Compromise (If Necessary)
If you can't get the contractor to completely back down, try to negotiate a compromise that minimizes the impact on your labor costs. Perhaps you agree to the "floating" method only for conduit runs of a certain size or larger, or only in specific areas of the structure.
Important Considerations
Safety First
Ensure that any method you use to support the conduit is safe and secure. The conduit must be adequately supported during the concrete pour to prevent movement or damage.
Documentation
Document everything – the original requirement, your concerns, the alternative solutions you proposed, and the final agreement. This is crucial for protecting your company in case of future issues.
In summary: The contractor's requirement, in its extreme form, is unusual and likely unnecessary for Rob Roy and PVC conduit, especially in smaller sizes. However, addressing their concerns through clear communication, expert documentation, and offering reasonable alternatives is the best approach. Good luck! Flag for review