Mounting generator transfer switch

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  #1  
Old 09-16-12, 01:33 PM
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Mounting generator transfer switch

I have a 7 Kw generator so my transfer switch can only power limited circuits. My existing breaker box has all the wires entering on the top. So my plan was to mount the 8 circuit transfer switch above the existing breaker box so I could just pull the wire for each existing circuit and move it to the transfer switch box. But that would put the transfer witch box higher than you can reach standing on the floor. Someone suggested code for a switch or breaker used as a switch can not be above 6' 7". But these are breakers not used as switches.

So is it code?
 
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  #2  
Old 09-16-12, 08:24 PM
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I'm far from a code expert, but I would say that it's not to code. At the very least, it'll be inconvenient if/when a breaker does trip.

I would mount the transfer switch to the left or right of the panel, connected with either a short PVC nipple or Greenfield. Then simply splice the 8 circuits and extend them to the transfer switch. Of course, be sure to use the same size (or larger) wire when you splice. An extra 8 splices in your panel should be fine... unless you have a really old small panel.
 
  #3  
Old 09-16-12, 09:12 PM
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my plan was to mount the 8 circuit transfer switch [panel] above the existing breaker box so I could just pull the wire for each existing circuit and move it to the transfer switch box. But that would put the transfer switch box higher than you can reach standing on the floor. Someone suggested code for a switch or breaker used as a switch can not be above 6' 7". But these are breakers not used as switches.

So is it code?
No. 6'7" (or some such distance AFF) to the top of the panel, IIRC, is a code requirement. Mount it to one side of your existing panel, as Zorfdt suggested, with the top of the new panel no higher than the top of your existing panel. If the cables that feed your critical loads won't reach, you can splice them in your main panel, as he also suggested, or you can mount a good-sized J-box above the xfer panel, move them to there, and add splices to single conductors to make them long enough to reach where they need to be.

Don't forget to splice everything in the cable - hot, neutral and ground. And, because bare conductors cannot be run through conduit, use green-insulated wire to extend the grounds.
 
  #4  
Old 09-20-12, 05:35 PM
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Thanks for the response. One side has a window and the other side is the corner wall of the garage. So it could be done on the other side of the window and maybe on the little corner wall but I was just looking for the logical location.
 
  #5  
Old 09-20-12, 05:47 PM
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One side has a window and the other side is the corner wall of the garage. So it could be done on the other side of the window and maybe on the little corner wall
Or it could be done by lowering your main panel enough to make the top of the highest breaker in the emergency panel no more than 6'7" AFF, with the J-box above that and conduits feeding down next to the new panel to the main. Or by mounting the new panel under the existing one. Lotsa ways to skin a cat.
 
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Old 09-20-12, 06:37 PM
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FYI The 6' 7" AFF measurement is to the highest circuit breaker handle, not the top of the panel. You could put it under it.

I recommend placing the panel around the corner and install a short piece of conduit and just loop the loads you want to have on the geny.
 
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Old 09-20-12, 07:59 PM
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FYI The 6' 7" AFF measurement is to the highest circuit breaker handle, not the top of the panel.
Thanks, Tolyn. I realized that after we'd gotten into it, but, for some reason, I hadn't said it.
 
  #8  
Old 09-23-12, 02:32 PM
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I've decided to put the panel on the short wall to the right side of the main breaker. So I'm looking for a box to mount above the main breaker to add wire to the existing circuits. Are there boxes large enough to have 18 or more wire entry holes? That would be for the 8 circuits driven by the generator and the 50 amp power from the breaker box to the transfer box.

Do I need to put all those wire in conduit running to the transfer box? The walls are all insulated and sheet rocked so would have to just run on top of the sheet rock.
 
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Old 09-23-12, 03:34 PM
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Is this a 'legacy' transfer switch that has double throw switches?



Or is it one of the newer 'subpanel style' which has actual breakers in it



If it's the newer style you won't need a box. Simply install a longer conduit between the main panel and the transfer panel and pull new wires. If it's the 'legacy' style, the flexible whip coming out of it should be long enough to get around the corner and into the panel if the panel is that close to the corner..
 
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Old 09-23-12, 04:44 PM
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Are there boxes large enough to have 18 or more wire entry holes?
Sure. A 12x12x4 should be plenty big. If you're asking about KOs, IDK. I always buy boxes with smooth sides and cut my own holes.
 
  #11  
Old 09-23-12, 08:44 PM
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Like Nashkat posted, they make many sizes of J boxes but in most cases they do not have KO's on them. You will have to drill your own using a 7/8" hole saw. I like using the Greenlee carbide tipped ones. They are spendy but work VERY well.

As I mentioned, and Matt also posted, installing a short piece of conduit and just running loops from the main panel to the generator panel would be easier and neater then a huge J-box. Just make all your splices in the main panel. Some panels, similar to Matt's pictures, already have the wires installed.
 
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Old 09-23-12, 09:24 PM
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I like using the Greenlee carbide tipped ones. They are spendy but work VERY well.
I have a set of those. I only use other brands if I'm working for someone else and they haven't agreed to replace mine if they are damaged on the job. In that case, mine stay in the truck and I enjoy seeing how little time it takes to turn the teeth on theirs white-hot.

After all, I replace mine when I'm working for myself. That's how I got to their job with a full set.
 
  #13  
Old 09-24-12, 04:09 AM
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Thanks again. I need the box to extend the existing 8 circuits removed from the original breaker panel to the transfer switch (which has new breakers and an auto main/generator switch). The generator is hardwired to the transfer switch through a conduit.

The box will let me pull the existing wires on those 8 circuits and extend the wire to reach the new transfer switch. All the existing wires enter the existing breaker panel from the top. It would be messy extending the wire in the existing breaker panel and running 8 new circuits from it since it's all sheet rocked in the wall.

So do I need BX cable for those 8 extended circuits or can NM cable be used without conduit?
 
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Old 09-24-12, 08:42 AM
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If your location allows NM-b, and the cables will be protected from damage (IE: inside the wall) Then it should be OK. Your "BX" will need to have a bonding strip along the steel jacket for a ground.
 
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Old 09-24-12, 10:05 AM
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It sounds like you're planning to mount the J-box on the surface, and bring the cables feeding the circuits you want to back up into it through the back, and then run spliced cables on the surface to your emergency power panel. Am I hearing that correctly?. Will that be in front of the area where the cables enter the panel, and block future access to that?

As far as running power on the surface goes, you might be allowed to run Type NM exposed since all of this will be so high, but that's up to your local jurisdiction. If it were mine, I would pull the eight circuits through four lengths of conduit, using individual conductors (no NM in conduit, except as sleeving - the jacket isn't rated for that). One insulated ground per conduit. All grounds bonded together and to the box in the J-box (install any small ground bar).

Or I would run eight pieces of MC, not BX - I want a real ground in each cable.
 
  #16  
Old 09-24-12, 01:34 PM
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Yes my plan was to mount the J box on the dry wall, run the existing wires throught the back and the new wires out the sides. The new transfer switch box would also be mounted on the dry wall.

So it sounds like the best thing to do is run single wires in conduit. I would have to decide how many wires I could fit inside each conduit.

Is there any preference to using metal or the gray plastic conduit?
 
  #17  
Old 09-24-12, 02:10 PM
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I like EMT, but I work with it all the time so I can bend it and such. PVC is a little more homeowner friendly, but you need to use a ground wire, and tends to be a bit tougher to push wire in. Most cases I will oversize the pipe by one size.

You can get 9 #12's in a 1/2" EMT. I suggest staying at no more than 9 wires in any pipe due to derating factors.
 
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Old 09-24-12, 04:00 PM
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I also prefer to use EMT, in part because I find it easier to work with than PVC. That said, I just glanced back to check my memory, and it looks like you will be mounting the MTS on the adjacent wall, at 90[SUP]o[/SUP] to the panel. Now I think I'm getting part of your reason for leaning toward cable.

I would run flex, aka Greenfield. It's conduit, and meets all requirements for conduit. It allows just as many wires in a given cross section as any other conduit. And it goes where you want it to without any more tools than your hands. It's essentially DIY MC.
 

Last edited by Nashkat1; 09-25-12 at 06:35 AM.
  #19  
Old 09-25-12, 06:25 AM
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Thanks again for all the great tips. I was looking for a large J-box but did not find one local and the price is very high. So it looks like I will install 3 smaller J-boxs and have one conduit from each running to the adjacent (90 deg) wall. Flex conduit would be nice since it and be clamped flat to the drywall.
 
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Old 09-25-12, 07:07 AM
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I was looking for a large J-box but did not find one local and the price is very high.
I don't know how many of the wires you're running are #14 and how many are #12, so I can't do a box fill calculation, but a deep 11B box has 46.7 in.[SUP][SUP]3[/SUP][/SUP] of capacity, and those are both commonly available and relatively inexpensive. No more than two of those should handle the 16 current-carrying conductors you need, You'd just have to bond all of the grounds in a couple of joined splices with a pigtail to the boss in the back of the box rather than installing a ground bar, but that saves you a buck or so too.
 
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Old 09-26-12, 12:29 PM
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Thanks again. I did find 11B boxes and will use those.

Can I use tandem circuit breakers to increase my 8 circuit transfer switch to more circuits?

My house has a lot of 15 amp existing circuits (outlets and lights) which I would want powered with the generator. These are very lightly loaded so would it just be better to splice some of those circuits into one new circuit or use tandem breakers?

My transfer switch is rated for 50 amps.
 
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Old 09-26-12, 12:34 PM
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Can I use tandem circuit breakers to increase my 8 circuit transfer switch to more circuits?
That is specific to the switch/panel. If you don't see that information on the label, post a picture of your switch/panel, and one of its label, and a link to the manufacturer's site, and we will look at it with you.

My house has a lot of 15 amp existing circuits (outlets and lights) which I would want powered with the generator. These are very lightly loaded so would it just be better to splice some of those circuits into one new circuit or use tandem breakers?
To determine whether you can safely combine any of those circuits, you need to do a load calculation for each circuit, using the maximum watt rating of each light fixture and a standard demand value for each receptacle.
 
  #23  
Old 09-26-12, 03:23 PM
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I will get some photos posted later. But I have a basic wiring question. There are two buss bars in the transfer swith box. The installation diagram shows one is used for neutal (white wires) and the other ground (green wires). These buss bars are not connected togeather and don't make contact to the metal case.

Shouldn't the ground buss contact the metal case?

It also shows the 50 amp supply lines from the main panel to have 4 wires attached to N1, N2 and two on the buss bar in the main breaker. So that would connect the two buss bars in the transfer switch togeather since one is white and one green.

The generator also has a 4 wire connection.
 
  #24  
Old 09-26-12, 04:16 PM
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Requested photos

First time I uploaded photos, hope this works.
 
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Old 09-26-12, 04:21 PM
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Shouldn't the ground buss contact the metal case?
One would think so. Are you sure it doesn't? Did the switch box come with a green screw to use for bonding it?

It also shows the 50 amp supply lines from the main panel to have 4 wires attached to N1, N2 and two on the buss bar in the main breaker. So that would connect the two buss bars in the transfer switch togeather since one is white and one green.
I'm not sure what you're asking. The neutrals and grounds should be bonded together once, at the service entrance. If the main distribution panel has a main disconnect, this is done there. In all other boxes, including subpanels, the box is bonded to ground and the neutrals are isolated from the box and ground.
 
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Old 09-26-12, 04:24 PM
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First time I uploaded photos, hope this works.
The upload worked great and the pictures are clear. But they don't tell us anything about tandem breakers. Check the manual or ask Generac.
 
  #27  
Old 09-26-12, 05:48 PM
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No grounding screw with the box. I checked continuity with an ohm meter and both buss bars connect to nothing. I guess they depend on metal conduit grounding the box. I will add a wire on the ground buss to a screw on the box.

Thanks for the education on how the neutral and grounds should be only hard wired at the main panel with the master switch.
 
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Old 09-26-12, 06:43 PM
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Can I use tandem circuit breakers to increase my 8 circuit transfer switch to more circuits?
Judging just from the circuit diagram I'd say that the panel does not accept tandem breakers. It's always best to ask the manufacturer if in doubt.
 
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Old 09-26-12, 08:07 PM
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I checked continuity with an ohm meter and both buss bars connect to nothing. I guess they depend on metal conduit grounding the box. I will add a wire on the ground buss to a screw on the box.
Not to insult your intelligence, but did you check the continuity setting on your meter by touching the probes together before you tested for bonding in the switch? That's an oversight I've made before
 
  #30  
Old 09-27-12, 08:33 AM
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No insult taken. Yes I do that oversight sometimes having the probes plugged into the wrong jacks on the meter. I will check again but I think I did verify meter was zero ohms by touching the probes. One of my meters will buzz if I select a function and the probes are in the wrong jacks.

I'm and electronics engineer so I really love the help I get on this forum doing things out of my profession.
 
  #31  
Old 09-27-12, 03:40 PM
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I checked for box continuity again and it definitely is floating on both buss bars. This is Generac's newer design box. It now uses 6 control wires when the old ones used 4. So the documentation is probably all new. Maybe it's only my box they forgot to install a jumper on but the document does not show any.

I wonder if the electrical inspection would have caught this error?
 
  #32  
Old 09-27-12, 04:21 PM
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I wonder if the electrical inspection would have caught this error?
Good question. IDK, but the idea of having a metal box in an energized system that isn't bonded to ground gives me the willies, frankly.

Glad you caught it.
 
  #33  
Old 09-30-12, 09:49 AM
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I've decided to use 3/4" flex metal conduit to wire the rest of my transfer switch. Do I need to put a sleeve into the conduit at each end? It would seem a good idea to prevent the conduit from cutting into the wires on a 90 deg. connector.
 
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Old 10-01-12, 09:54 AM
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I've decided to use 3/4" flex metal conduit to wire the rest of my transfer switch. Do I need to put a sleeve into the conduit at each end?
Yes. All flexible metal conduit needs an anti-short bushing - aka a "red-eye" - in each cut end before being clamped into a connector. It's the same as it would be for BX or MC, just bigger.
 

Last edited by Nashkat1; 10-01-12 at 09:33 PM.
  #35  
Old 10-01-12, 07:36 PM
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I've decided to use 3/4" flex metal conduit to wire the rest of my transfer switch. Do I need to put a sleeve into the conduit at each end?
It's a good practice, but I don't think they are required for flexible metallic conduit or MC cable. Here they are commonly call "redheads".
 
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Old 10-01-12, 09:37 PM
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I don't think they are required for flexible metallic conduit or MC cable
Gotta have them here or they'll fail you in a heartbeat. And even though I trim my cut ends with a BX trimmer, I wouldn't dream of finishing the assembly without one. A short waiting to happen, IMO and IMX.

Tip: Turn the ASB so that the opening in it is opposite the long point of the flex coil.
 
  #37  
Old 10-02-12, 12:07 PM
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Dang....those things are hard to find. I guess the most common term is "anti-shorting bushing". I had to order them online. Found this info:

http://www.mikeholt.com/documents/mo...Bulletin90.pdf

So what is the difference between MC and AC? You guys use so many short abreavations, it's hard for the layman to follow things.
 
  #38  
Old 10-02-12, 01:18 PM
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MC has a full ground cable inside and may or may not have a bonding strip. AC has no ground wire but a bonding strip so the sheath can be used as a ground.
 
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Old 10-02-12, 01:37 PM
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those things are hard to find.
That's strange. I can buy 'em by the bag at every big box store and supply house here, including every one I've looked for them in in Maryland.

I guess the most common term is "anti-shorting bushing".
Or "anti-short bushing." Sorry I didn't think to put a link on that in my earlier post.
 
  #40  
Old 10-02-12, 01:56 PM
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The bushings are not in our Lowes or two hardware stores I checked. I bought the metal flex conduit at Lowes so you would think they would stock them.
 
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