30A Generator Inlet Box - 10awg vs. 8awg

[Ryanm00085]

I am installing a Reliance Controls PB30 generator box to power a panel from a 7000 watt generator. my debate is whether or not to use 10awg or 8awg wire. I know 10awg should be sufficient enough, but I feel like 8awg would keep any heat down. The run is only 50 feet, 35 inside which I will run romex and 15 feet outside, which I plan on using PVC and THHN with a junction box on the inside wall. I read the instructions and of course it says use either 10awg or 8awg. I just feel if the panel is drawing close to the max load, it would be better to use 8awg to cut back on the heat of the wire, but of course 10awg is cheaper and easier to work with. Any suggestions or ideas?

 

[charlie b]

A quick voltage drop calculation tells me you would get 2% VD with #10 and 1% VD with #8. To me, that does not seem to warrant the extra expense and installation work, so I would go with #10. Welcome to the forum.

 

[adamant]

30A generator inlet

30A generator inlet

I would think that being a 50 foot run you'd probably want to go with the 8 AWG just to be on the safe side. Usually there is a sizable difference between 10 AWG and 8 AWG cable, but it looks like this site sells pre-fabricated generator cables with the 8/4 wire and the price looks comparable to most 10 AWG cables:
- Chris

 

[qcroanoke]

Any suggestions or ideas?

If you are making the cord up check what size wire the lugs are good for. I got turned back when all I could find was plugs and receptacles good for #10.

 

[iwire]

I have to be honest, the thought of using 8 AWG for a 50 foot run for a load that can't be more than 30 amps short term or more than 24 amps continuous sounds crazy to me.

10 AWG is rated 35 amps.

Besides a waste of money I see issues making the connections as qcroanoke mentions.

 

[ActionDave]

10AWG for me all day long. I wouldn't think of using 8AWG unless it was the middle of the night and I had nothing else on the truck.

 

[GerryB]

10AWG for me all day long. I wouldn't think of using 8AWG unless it was the middle of the night and I had nothing else on the truck.

Ditto that. Especially when you can buy a premade cord, I just saw one, 75', #10 wire.

 

[Ryanm00085]

Its not the actual cord im running. Its from the panel to the the inlet box with the male plug in it. Im running Timex in the basement then thhn in conduit outside to then outlet. Then I have a 25' 10age cord that goes from the inlet plug to the generator. I figured 8awg would cut back on heat if we r pulling almost a full load. The inlet is rated for 30amp and will will on a 30 amp breaker.

 

[jaylectricity]

What kind of heat are you expecting here on conductors that aren't even using their full ampacity?

 

[Ryanm00085]

Well that's what I am trying to figure out. I figured if we were pulling a decent 25A load, powering it with 8awg would keep the heat down as opposed to running 10awg. Just thought oversizing the wire would have been a better idea for long term. If 10awg is sufficient I will stick with the 10awg.

 

[winnie]

As a theoretical matter, the #8 conductors have lower resistance and will run cooler than the #10 conductors at the same load. Based on the calculations used to derive NEC table 310.15, when carrying 30A, you would expect the #10 conductors to reach a temperature of 60C, and the #8 conductors to reach a temperature of 47C.

As a practical matter: the calculations used to derive NEC table 310.15 are very conservative and assume fairly high thermal resistance, and assume heat being generated by 3 conductors. It is quite rare for installed circuits to actually reach the expected temperatures because the calculations are so conservative (but it does happen, in insulated cavities with multiple cables in the same hole, for example). So the 'theoretical' 13C difference is likely to be much smaller in practice. On top of this, the wire that you run is probably rated at 90C.

IMHO just run the #10, and if you want to burn some extra money spend in on the best quality inlet connectors. The most common cause of heating for plug in circuits is bad contact at the connections.

-Jon

 

[SceneryDriver]

I am installing a Reliance Controls PB30 generator box to power a panel from a 7000 watt generator. my debate is whether or not to use 10awg or 8awg wire. I know 10awg should be sufficient enough, but I feel like 8awg would keep any heat down. The run is only 50 feet, 35 inside which I will run romex and 15 feet outside, which I plan on using PVC and THHN with a junction box on the inside wall. I read the instructions and of course it says use either 10awg or 8awg. I just feel if the panel is drawing close to the max load, it would be better to use 8awg to cut back on the heat of the wire, but of course 10awg is cheaper and easier to work with. Any suggestions or ideas?

Is there any possibility that the generator might be upgraded in the future to a size that would require the #8 wire? The cost difference isn't tooooo much for upping the wire size over that length of run. I'd bet that the time you've spent deciding this ended up being worth more than the difference in copper.



SceneryDriver

 

[ActionDave]

Is there any possibility that the generator might be upgraded in the future to a size that would require the #8 wire? The cost difference isn't tooooo much for upping the wire size over that length of run. I'd bet that the time you've spent deciding this ended up being worth more than the difference in copper.



SceneryDriver

Fifty feet can be pulled in about fifteen minutes, including a couple drinks of water. Making up 10AWG is always easier than 8AWG.

 

[SceneryDriver]

Fifty feet can be pulled in about fifteen minutes, including a couple drinks of water. Making up 10AWG is always easier than 8AWG.

Fair enough. I was referring to the time he's spent thinking this over.



SeneryDriver