[RE-wrenches] cable spacing in trenches

[Ray Walters]

Drake;

I had trouble finding that reference, then I found it in the back in 
Annex B. I think that would apply to the ampacity of the DC line, but 
then for the 12.47 Kv line, I believe you would need Figure 310.60 which 
then references Tables 310.60 C (77) thru Table 310.60 c (86)
Without knowing more details, it looks like Jerry would need 24" spacing 
(see details 6,8, or 10).
This seems like an issue that you'd want a PE to double check and sign 
off on, as that is a fairly high AC voltage, and there could possibly be 
a significant induced AC voltage on the DC line (especially if its a 
long shared ditch).

Ray Walters

On 11/6/2011 8:36 AM, Drake wrote:
> Check out Figure Figure B.310.15(B)(2)(1)
>
>
>
> At 07:43 AM 11/4/2011, you wrote:
>> Separation is an issue the NEC does not address clearly .However, 
>> please make sure you allow adequate room to repair the conduit if 
>> damaged, and 12' seems to be the magic number. I lso had no luck 
>> looking in 490.
>>
>> NEC 300.4(C)(2)(e) also seems a bit relevant where it allows for 
>> conductors of different voltage ratings in manholes "if the 
>> conductors of each system are permanently and effectively separated 
>> from the conductors of the other systems...", but again this may be 
>> referring to separate trenches with different system voltage ratings 
>> entering the same manhole for tapping, allowing access for 
>> maintenance or other uses.
>>
>>
>>
>> On Thu, Nov 3, 2011 at 5:42 PM, Jerry Caldwell <solarcowboy at yahoo.com 
>> <mailto:solarcowboy at yahoo.com>> wrote:
>>
>>     Can anyone direct me to the NEC article that stipulates how many
>>     inches of separation must be between cables operating at
>>     different voltages?
>>
>>     I have a project with PV combiner box home runs at 1,000 volts DC
>>     in the same trench with 12.47 kV cables.  Table 300.5 shows
>>     minimum cover requirements for direct burial cables, but this is
>>     the distance beneath grade the cables must be.  Is there anywhere
>>     in the code that calls for a minimum separation distance between
>>     cables at different voltages?
>>
>>     Thanks,
>>     Jerry Caldwell
>>
>>
>>
>>
>>     From: Marco Mangelsdorf <marco at pvthawaii.com
>>     <mailto:marco at pvthawaii.com>>
>>     To: 'RE-wrenches' <re-wrenches at lists.re-wrenches.org
>>     <mailto:re-wrenches at lists.re-wrenches.org>>
>>     Sent: Thursday, November 3, 2011 2:27 PM
>>     Subject: [RE-wrenches] under performing Enphase inverters
>>
>>     For the first time, several weeks ago, after 40-50 Enphase
>>     installs, we've come across at least two M210s that we putting
>>     out consistently lower outputs than their immediate neighbors.
>>
>>     We replaced the two mods first, which made no difference.  Then,
>>     in consultation with Enphase, replaced the M210s.  After
>>     replacing them, the power output was as it should be.
>>
>>     Now I've got another suspect system with several underperforming
>>     mods out of (36).
>>
>>     Has anyone else had this experience?
>>
>>     Thanks,
>>     marco
>>
>>
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>> -- 
>> James B Rudolph
>> NABCEP Certified PV Installer
>>
>>
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>
> Drake Chamberlin
> ATHENS ELECTRIC LLC
> OH License 44810
> CO license 3773
> NABCEP Certified PV
>
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