555.13(B)(4)(b)

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hardworkingstiff

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Wilmington, NC
In trying to better understand this section, I found out from someone at NFPA (lost his email when I crashed my PC, dumb me) some interesting information. This junction box requirement 1st showed up in 1960 and it was clear at the time that the suggestion was to bring a feeder out to the dock, then branch off to catch the receptacles and lighting. The junction box was intended to be the location of all of the taps to the feeder. This wiring method was suggested in lieu of individual branch circuit wiring to each receptacle. Back then I don't think we had 200-amp rated power centers to deal with.

The wording changed a couple of times in 1968 and 197? (sure wish I didn't lose that email). The original intent seemed to have been lost in the rewording.

Locally, (Wilmington, NC) the inspectors are requiring these junction boxes be installed. It seems to me to serve no purpose, and it is just another corrosion point. They have agreed to let a panel immediately adjacent to the ramp down to the floating dock to serve as this junction box, but that is not always practical. The engineer I've worked with does not understand why this JB is required, and agrees it makes no sense.

Does anyone have any experience discussing this section? I would love to understand the reason why it is in here.

Thanks,
Lou
 
Re: 555.13(B)(4)(b)

I posted this in the wrong forum and when it moved to this one, it was a couple of day old. So I responded to myself to hopefully get some ones attention that may know more about this.

Thanks
 
Re: 555.13(B)(4)(b)

Is it clear to you that you only need this junction box (actually, two of them, one on land and one on the dock) when you are using portable cables (i.e., not a Chapter 3 wiring method), and when the reason you are using portable cables is that you need the flexibility (i.e., because it is a floating dock, and because the tides will cause the dock to move with respect to the land)?

The pair of junction boxes creates a permanent installation at the "joint" between the moving (i.e., floating) dock and the stationary land. You bring landside cables to one junction box. You continue onto the dock from the other junction box. Between the two junction boxes you have essentially a "jumper cable," and it allows for movement at the joint. You can add or remove cables as needed at the terminal blocks within the junction boxes, but you never have to touch the permanent part of the installation, the "jumper cables."

I did a design once that featured this type of junction box. I recall that I needed four junction boxes for each floating dock. That was because each floating dock had a long access ramp. I had to allow for tidal movements in the joint at the top of the ramp and for tidal movements in the joint at the bottom of the ramp. From that point onto and throughout the floating dock, I ran primary 3-phase 3-wire, using a Chapter 3 method (conduit built into the center of the floating dock itself), to step-down transformers located throughout the dock.
 
Re: 555.13(B)(4)(b)

Originally posted by charlie b:
Is it clear to you that you only need this junction box (actually, two of them, one on land and one on the dock) when you are using portable cables (i.e., not a Chapter 3 wiring method), and when the reason you are using portable cables is that you need the flexibility (i.e., because it is a floating dock, and because the tides will cause the dock to move with respect to the land)?
Click to expand...
Yes Charlie, it is clear to me. It also makes me scratch my head because if you were to use flexible conduit between a fixed pier and floating dock, LB's or C-condulets on each section, you would not be required to install junction boxes. This makes me question the reasoning behind the requirement when using portable power cable.
 
Re: 555.13(B)(4)(b)

I don't know much about hardware. I couldn't tell an "LB" from a "c-condulet" if you gave me two guesses and a "lifeline" phone call. But I do know that you would have to attach a portable cable to something that is secure at each end. You would not want to just have a support hanger, and let the cable slide in and out (across the hanger) every time the tide goes in and out. There will be some type of strain relief at the point the portable cable enters the junction box. That will take the weight of the cable as it rises and falls with the tide. If you did not have a junction box to perform this role, what would you use?

But why require terminal blocks to land the conductors of the portable cable and to land the conductors of the supply (or load) cables? I am not sure, and I think this is your real question.

All I can offer is this: Washington State Administrative Code (WAC 296-46B-555) revised the way 555 would apply here, in that portable cable can be used for the entire length of the run, even if it is within (not just under) the piers. That rule also states that NEC 555.13(B)(4)(b) does not apply (i.e., no junction box is needed). That tells me that if anyone in another State wanted to run cables through the center of the piers, they would have to use a Chapter 3 method. That would require a transition from the suspended portable cable to the conduit run. I don't know of an easier, more secure, or "cleaner" way to accomplish that transition than to use a junction box with terminal points.
 
Re: 555.13(B)(4)(b)

CHARLIE, THAT'S GREAT!!!! (yes I'm shouting).

That's exactly what we are doing here, using it for the whole wiring system. Are you able to give me a link to that administration code?

Thanks Charlie.

<edit> I found the link, thanks.

[ November 17, 2005, 12:27 PM: Message edited by: hardworkingstiff ]
 
Re: 555.13(B)(4)(b)

Originally posted by hardworkingstiff:I found the link, thanks.
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Glad to be of assistance. I see from your original post that you are on the other side of the country from Washington State. Does NC have a similar local rule?

In case anyone else is interested, here is the related WAC.

[ November 17, 2005, 12:49 PM: Message edited by: charlie b ]
 
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