Re: UG Conduits Separation NEC recommended Distance

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Lightninarrester

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Re: UG Conduits Separation NEC recommended Distance

Guys, does anyone know the NEC recommended separation distance between different voltage classes in ductbanks, for example the recommended distance between a MV conduit and a low voltage or instrumentation/communication conduit.
 
Re: Re: UG Conduits Separation NEC recommended Distance

The NEC does not provide any recommendations of this type. The 7.5 inch separation that is shown on certain figures, such as FIgure 310.60, is neither a recommendation nor a requirement, nor for that matter a minimum acceptable distance. I will acknowledge that some authorities view that 7.5 inch distance as a minimum distance, but the NEC makes no statement to that effect.
 
Re: Re: UG Conduits Separation NEC recommended Distance

I haven't realy had any reason to consider this page before. Are the details in figure 310.60 referenced by other tables or sections? It looks like all the horizontal dimensions have no purpose. And details 6, 9 and 10 are nothing but horizontal dimensions.

There has to be a purpose. There just has to be.

And what about detail 5? What's that about? It's a dot! Detail 5 is nothing but a dot!

:confused: :confused: :confused:
 
Re: Re: UG Conduits Separation NEC recommended Distance

Originally posted by physis:
And what about detail 5? What's that about? It's a dot! Detail 5 is nothing but a dot!
Click to expand...
Nothing but a dot? ;)
 
Re: Re: UG Conduits Separation NEC recommended Distance

Well, it's a really nice dot. It's definately one of the better dots I've seen. I mean, I've seen a lot of dots, and this one's well above par. I'd recommend this dot! :cool:
 
Re: Re: UG Conduits Separation NEC recommended Distance

But SAm what you don't see is inside of that dot is three current carrying conductors and a grounding conductor so one Dot can supply much power. :D
 
Re: Re: UG Conduits Separation NEC recommended Distance

I did a medium resolution scan and blew it up 10 times. I think the three dots are just a coincidence.

NECDetail5.jpg
 
Re: Re: UG Conduits Separation NEC recommended Distance

Originally posted by physis:Are the details in figure 310.60 referenced by other tables or sections?
Click to expand...
Start at Table 310.77 and go forward. You will see where and how these details are used.
 
Re: Re: UG Conduits Separation NEC recommended Distance

Originally posted by physis:And what about detail 5? What's that about? It's a dot! Detail 5 is nothing but a dot!
Click to expand...
The legend for Figure 310.60 defines that dot as representing a cable or cables. It's the same "dot, just a dot" that appears in all the other details. Detail 5 is the same as Detail 1, but without the extra "window dressing." :D
 
Re: Re: UG Conduits Separation NEC recommended Distance

Thanks guys for the Dot clarification ;) , is there any other code requirement or inustry standard or acceptable practice for minimum distance clearnce between different voltages in UG conduits :confused: .
 
Re: Re: UG Conduits Separation NEC recommended Distance

The reason I see it as being so completely pointless (pointless :D ) Charlie is that the dot is defined in the other details as well. So it isn't needed.
 
Re: Re: UG Conduits Separation NEC recommended Distance

I don't think there is Lightninarrester but I don't do many underground runs and I'm not all that informed on it.

Sorry about the dot. :D
 
Re: Re: UG Conduits Separation NEC recommended Distance

Originally posted by physis: The reason I see it as being so completely pointless Charlie is that the dot is defined in the other details as well. So it isn't needed.
Click to expand...
But if it were not there, some overly zealous person of the ?AHJ persuasion? ;) would conclude that the code does not allow a single, buried cable, on the grounds that there is no detail that shows one.
:eek:
 
Re: Re: UG Conduits Separation NEC recommended Distance

Charlie,
The NEC does not provide any recommendations of this type. The 7.5 inch separation that is shown on certain figures, such as Figure 310.60, is neither a recommendation nor a requirement, nor for that matter a minimum acceptable distance.
Click to expand...
It is my opinion that if the spacing shown in Table 310.60 are not used, then you cannot use the ampacities in Tables 310.77 through 310.86. If you use other duct back designs, then you must calculate the conductor ampacity per 310.60(D).
Don
 
Re: Re: UG Conduits Separation NEC recommended Distance

Oh, I agree, Don. But the question related to recommended separation, and I was only addressing that question.

I have seen people try to enforce, or try to rely too heavily upon, the 7.5 inches in those details. All I am saying is that the 7.5 inches is neither necessary nor sufficient to cause the installation to be acceptable.
 
Re: Re: UG Conduits Separation NEC recommended Distance

The other thing than many miss is that Figure 310.60 specifies a maximum burial depth of 36" to the top of a cable or 30" to the top of the duct bank. Greater depths also require that the ampacity be calculated under engineering supervision. The only good thing is that most of us don't have to use these tables very often as they only apply to 2000 volts and up.
Don
 
Re: Re: UG Conduits Separation NEC recommended Distance

NEC has no recommended separation distances for HV, MV, LV and communication/control conduits in UG duct banks. Industry standards (IEEE 518 "Guide to Minimize Noise Inputs to Controllers...") suggested different separation distances based on the voltage level and installation method: 12" between MV & control in rigid steel conduit, 84" between cables in air, 26" between steel cable trays, etc.

Experience has shown that these separations are very conservative. IEEE 518 has been withdrawn for various reasons, so there is not an industry standard or guide that recommends separation.

IMO keep the LV control and communications in RGS conduit or run them in armored cable. Keep at least 12" separation between high current power cables and control cables. We always use different duct bank and manhole systems for MV cable (4.16 kV and up) and 600 V and control/communications systems and combine them only when absolutely necessary. We just don't like having a 15 kV cable in the same manhole with telephone and lighting circuits, even when cable spacing is maintained and controlled by lashing them on racks (racking) and the HV cables are covered with fireproofing tape.
 
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