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Old 01-26-2019, 12:14 AM   #1
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Default 320 amp service and portable generator

Customer has dual 200 amp main panels with a 320 amp service. Bought a expensive 7500 watt ng generator for backup power. Whatís the best way to feed this?

Right now thinking an indoor mounted 400 amp transfer switch and a 30 amp inlet on the outside. Price tag is coming out to $1,200. For his total price with generator and gas it makes sense to just get a small standby gen.
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Old 01-26-2019, 12:59 AM   #2
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For a generator that small I'd do a small sub panel for the circuits he wants during an outtage. Maybe a 16 or 24 circuit panel. No way on a 7500 watt generator will you get to use everything from the 320 amp service...

Unless you meant to say 75 000 watt instead.

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Old 01-26-2019, 04:25 AM   #3
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Installing a 400 amp transfer switch should cost way more than $1200. The switch alone is extremely expensive and you have to rework the entire service.

But forget that idea altogether. You should just install an interlock on one of the 200 amp main panels. Backfeed a 30 amp breaker and run a 10-3 wire to an inlet.

Then just switch any circuits that he wants during an outage to the panel with the interlock.
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Old 01-26-2019, 06:35 AM   #4
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Quote:
Originally Posted by Locknutz View Post
Customer has dual 200 amp main panels with a 320 amp service. Bought a expensive 7500 watt ng generator for backup power. Whatís the best way to feed this?

Right now thinking an indoor mounted 400 amp transfer switch and a 30 amp inlet on the outside. Price tag is coming out to $1,200. For his total price with generator and gas it makes sense to just get a small standby gen.
Ronk makes a very inexpensive double throw in both service rated and non-service rated:

https://www.ronkelectrical.com/meter...tches-7416.php
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Old 01-26-2019, 06:36 AM   #5
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I have a customer that wants to do the same thing, run a 320A/dual 200 service with a portable generator. Instead, I gave him a price on a standby 25KW natural gas generator with dual 200A, service entrance rated transfer switch. He hasn't decided yet.
The problem with a portable generator is, most are not rated for computer, electronics and circuit board use, and they're loud. The potable Honda EU7000iS is a good choice but costs almost $5,000. Another problem is gasoline storage.
For a $5,600, I can purchase both the 25KW and transfer switch.
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Old 01-26-2019, 06:40 AM   #6
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Its my opinion that people have a little too much to drink and end up buying a generator for whatever reason.
They then sober up when they find out what they bought is wildly inappropriate for what need.
People somehow believe purchasing a generator is like buying a washing machine and think they can just call someone to install it.
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Old 01-26-2019, 06:57 AM   #7
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With the correct install and a customer who understands how manage loads, it could be ok, or a couple of selected circuit panels. Making people understand you need to run the portables regularly and use some fuel stabilizer seems to be one of the bigger challenges. I know he mentioned his was ng, but most aren't.
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Old 01-26-2019, 07:36 AM   #8
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Quote:
Originally Posted by Southeast Power View Post
Ronk makes a very inexpensive double throw in both service rated and non-service rated:

https://www.ronkelectrical.com/meter...tches-7416.php
just for the sake of assuming... I assume the OP's service is fed in
parallel from the 320 amp meter socket enclosure to the 2 200
amp panels.

Does the Ronk product you posted , which is rated single phase @ 400
amps , have parallel lugs in it (or ate least able to accomodate them?)
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Old 01-26-2019, 07:46 AM   #9
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Quote:
Originally Posted by lighterup View Post
just for the sake of assuming... I assume the OP's service is fed in
parallel from the 320 amp meter socket enclosure to the 2 200
amp panels.

Does the Ronk product you posted , which is rated single phase @ 400
amps , have parallel lugs in it (or ate least able to accomodate them?)
Yes it will take one big one or two smaller.
I have installed at least three of these from what I can remember. They are cheap, only a few hundred bucks and a decent size.
The major brand double throws are massive in size and at least 4x the price.
I purchase these through my electrical wholesaler as the price is about the same. Ronk, like most that sell to the public protects the electrical supply houses.
I didn't take very many pic of the 400 but have a few of a 200 we installed.
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Old 01-26-2019, 07:53 AM   #10
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Quote:
Originally Posted by Southeast Power View Post
Ronk makes a very inexpensive double throw in both service rated and non-service rated:

https://www.ronkelectrical.com/meter...tches-7416.php
I don't know how I've never seen this, thanks for sharing.
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Old 01-26-2019, 08:11 AM   #11
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This is a pic of an installed


I cant deal with this sideways pic thing but.
We came out of a 320 meter, installed a 400amp main disconnect per the engineer. I could have used the SE model.
We then fed the utility side of the Ronk Switch. Out of there, we fed each of the existing 200 amp mains.
FWIW, this one was an open delta.

One more thing.
The utility side is connected to a set of 4/0 size camlocks at the bottom of the enclosure.
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Old 01-26-2019, 08:16 AM   #12
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This one is a 200 amp.
Fed out of a meter-main combo. We fed the Ronk out of the feedthrough lugs.
the load side feeds a 200 amp main lug interior loadcenter.
This setup gives us a few circuits ahead of the generator for whatever might be needed outdoor such as a fixture indicating if utility power was restored, battery charger, heater, etc.


Last edited by Southeast Power; 01-26-2019 at 08:18 AM.
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Old 01-26-2019, 08:24 AM   #13
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Damn, I just looked at the price on them. Insanely high pricing!
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Old 01-26-2019, 08:41 AM   #14
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Put a mechanical interlock in each breaker panel, a wire out of each panel to a J-box, and a cord from there with a plug to plug into the generator
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Old 01-26-2019, 06:25 PM   #15
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Quote:
Originally Posted by John M. View Post
Put a mechanical interlock in each breaker panel, a wire out of each panel to a J-box, and a cord from there with a plug to plug into the generator


I think this is the most cost effective approach. Splitting the 30 amp inlet feed onto two 30 amp beakers with interlocks in each panel.
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Old 01-26-2019, 06:31 PM   #16
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Quote:
Originally Posted by John M. View Post
Put a mechanical interlock in each breaker panel, a wire out of each panel to a J-box, and a cord from there with a plug to plug into the generator
Quote:
Originally Posted by Locknutz View Post
I think this is the most cost effective approach. Splitting the 30 amp inlet feed onto two 30 amp beakers with interlocks in each panel.
I donít like that idea because if there is a bastard splice anywhere into the house you could backfeed into the grid when only switching one of the panels over.

Generally doing one panel should be enough for them, especially if you switch some circuits over to it.
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Old 01-26-2019, 06:34 PM   #17
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Quote:
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I donít like that idea because if there is a bastard splice anywhere into the house you could backfeed into the grid when only switching one of the panels over.



Generally doing one panel should be enough for them, especially if you switch some circuits over to it.


Trying to picture this in my head? Example? Been working all day maybe my brain is too fried.
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Old 01-26-2019, 06:40 PM   #18
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Quote:
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Trying to picture this in my head? Example? Been working all day maybe my brain is too fried.
If you flip one interlock that will isolate that panel from the grid, but the other panel will still be connected to the grid and half of the circuits in the house.

I have found bastards splices in many houses in which two hots from completely different circuits were spliced together in a box. Nothing happened because they were on the same phase. But if this type of splice is in their house, when flipping only one interlock they could backfeed out into the grid. Or when the power returns it could feed through and destroy the generator.

Itís only 30A max, feeding a single 200A panel should get them what they need within the limits of the generator.
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Old 01-27-2019, 12:07 AM   #19
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Quote:
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If you flip one interlock that will isolate that panel from the grid, but the other panel will still be connected to the grid and half of the circuits in the house.



I have found bastards splices in many houses in which two hots from completely different circuits were spliced together in a box. Nothing happened because they were on the same phase. But if this type of splice is in their house, when flipping only one interlock they could backfeed out into the grid. Or when the power returns it could feed through and destroy the generator.



Itís only 30A max, feeding a single 200A panel should get them what they need within the limits of the generator.
But with an interlock on only one panel this is still a possibility no?

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Old 01-27-2019, 06:27 AM   #20
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First, you need to get two dryer cords...
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