Wireway support intervals

[chrisplusian]

I have always supported wireway at ends and at five foot intervals. 376.30(A) says "wireways shall be supported where run horizontally at each end and at intervals not to exceed 1.5m (5ft) or for individual lengths longer than 1.5m (5ft) at each end or joint, unless listed for other support intervals. The distance between supports shall not exceed 3m (10ft).

I have notes from when I did my apprenticeship in the 2002 code cycle. The code read exactly the same. I drew a picture, in my notes, to show if it was a long run of wireway that you had to support ends and at 5' intervals and another picture to show a single section of wireway used which was over 5' but less than ten that it only had to be supported at the ends. My notes said "this is only allowed for single isolated sections". My question now, comes from working with an industrial customer who said if the wireway sections are 10' that they only have to be supported at the joints, because the code says "or for individual lengths longer than 1.5m (5ft) at each end or joint. They make a good point.... if when the code says "for individual lengths" they meant a single section of wireway then why would it include joints?

I am now confused about the requirement. I even bought the mike holt "understanding the code" book and looked in there. He did a sad explanation of the requirement. He addressed the simple part... the one I have always used. The part of the requirement that starts at "or" is hard to understand, and he did not address.

My question: What exactly does the second part of the requirement (or for individual lengths longer than 1.5m (5ft) at each end or joint, unless listed for other support intervals) mean?

 

[Frank W]

If the wire passes through a penetration, say wood, horizontally, then that counts as supporting means. You definitly have to have your ends secured before/after entering or exiting a box. Within 3'.

 

[tom baker]

Perhaps look at the installation instructions. ten feet is way to long for support or wireway, I assume you are referring to wiremold

 

[Frank W]

320.30 (C) Supporting. Unless otherwise permitted, Type AC cable shall be supported at intervals not exceeding 1.4 m (41⁄2 ft). Horizontal runs of Type AC cable installed in wooden or metal framing members or similar supporting means shall be considered supported where such support does not exceed 1.4-m (41⁄2-ft) intervals.

 

[infinity]

I'm confused is this about wireways, Wiremold, or AC cable?

 

[electricman2]

320.30 (C) Supporting. Unless otherwise permitted, Type AC cable shall be supported at intervals not exceeding 1.4 m (41⁄2 ft). Horizontal runs of Type AC cable installed in wooden or metal framing members or similar supporting means shall be considered supported where such support does not exceed 1.4-m (41⁄2-ft) intervals.

I thought the OP said wireway, not type A/C cable

 

[jusme123]

You must look at both the code and manufactures support requirements, and satisfy both to be compliant. JMO

 

[Carultch]

My question: What exactly does the second part of the requirement (or for individual lengths longer than 1.5m (5ft) at each end or joint, unless listed for other support intervals) mean?

"Unless listed for other support intervals" means that the manufacturer's product documentation will provide a support interval other than 5 ft. It could allow you to support at intervals greater than 5 ft, or it could require you to support it tighter than 5 ft. In otherwords, 5 ft is the default, and the manufacturer has the onus of proof otherwise.

Alternatively, this rule also allows you to support the factory lengths immediately at each end or splice joint. This is common, when there are factory holes in the back of the wireway, intended for fastening it. Also common, if you are using wire trough instead of a wireway. The difference being that troughs have built-in end walls / need nipples to join, while wireways use wireway joints to form longer assemblies and closure caps to terminate. Nipples are not structural, so wire trough sections need to each be supported without depending on their neighbors. From what I've seen in practice, factory holes in wireways/troughs are about 2 inches from both ends of factory lengths. The maximum support interval when aiming for ends of straight sections is 10 ft, and is only an issue in practice if you could find a factory length longer than 10ft in the first place.

As an example, suppose you were building a 32 ft long wireway out of 4x 8ft factory lengths. The dots indicate the splice joints between each factory length. The triangles indicate the support locations. The top picture shows a solution using the 5 ft support interval uniformly, and located independently of the splice joints. The bottom picture shows a solution using the strategy of supporting each factory length immediately adjacent to each joint/end.

 

[chrisplusian]

@Carultch Thank you! I think what you are saying lines up with what I did when I was an electrician. We would do troughs and not adhere to the 5' variant, but they were often just at panels or for motor taps at wastewater plants. I am dealing with a design now that requires seismic support hangers and they are very costly. The wireway will be about 300-375 feet. The question about 5 foot verse ten foot intervals is really being driven by a desire to keep cost down, but my gut said it wasn't acceptable. I guess my best hope to keep cost down is looking for a wireway that is listed for 10' intervals.

 

[chrisplusian]

Perhaps look at the installation instructions. ten feet is way to long for support or wireway, I assume you are referring to wiremold

I am actually of the opinion 5' intervals is correct. This is dealing with a controls installation in a food grade plant in California which will have 300-375 feet of stainless wireway. The customer insists on lay in wireway cause their maintenance crew has to use it to change out production lines frequently (every two years or so). We have to have special seismic supports fabricated and installed through the finished roof structure. The cost for all the supports and structural work is in the hundreds of thousands. Someone on the customers team saw the 10' part and said "Oh we can buy ten foot sections and only do one hanger per joint as long as we make two tie points so each "joint" has support. I said that was not ok as far as I knew. I was asking here to try and find an advocate for their side of the argument. I personally disagree, but when I do I try to disprove my own argument with valid logic. So far I cannot prove their side of things, and I have reached out to several US wireway distributors to find one who will approve the 10' interval and they all laugh.

 

[chrisplusian]

I'm confused is this about wireways, Wiremold, or AC cable?

Wireway