Replies

1. 
   toddlen1875 | Jul 18, 2002 04:04am | #1

   I would feed it 100 amps .  number 2 ccpper in a flex conduit would be my first choice, unless it is close to the main panel, then conduit would look better.  yes the only thing connected to the ground bus will be the wire from the main.  make sure the neutral bar is isolated from the box.  why are there no grounds in the panel ? is the existing wire bx or old romex.  are you  sure the there was a ground to the box in the outlets you changed.  something you may think about is using the old 100 amp box for a junction box instead of a sub panel.  hope this helps if I missed something write back and i will try to reply shortly.  What happened to the down the stream, up the crevis guy?

1. 
   ahneedhelp | Jul 18, 2002 05:11am | #2

   Thanks for the reply, Todd -

   In the aftermath of my heatstroke from the attic, I failed to paint an accurate picture of what's going on in the old box and also not clear on my question.

   The old service entrance cable consists of two thick cables, a black and a red, and one bare strand.

   The black and red each go to the two connection on the main 100-amp breaker. The strand is connected to the neutral bus bar.

   When the service is upgraded to 200-amps to a new panel, it will feed the old panel which will continue to serve most of the lighting circuits. The feed, if I remember correctly from a previous project, will have two hots, a neutral and ground.

   So.....would the standard procedure be to mount a separate ground bus bar ?

   (The new load center will also have separate neutral and ground bus bars because there is a main disconnect outside next to the meter.)

   What's confusing me is with the panel being made of metal, there is still a path between the neutral bus bar and the newly installed ground bus bar....

   A new load center usually comes with a bonding screw that is used for certain situations, which I am not clear on.

   Thanks,

   Alan

1. 
   CPopejoy | Jul 18, 2002 05:47am | #3

   Alan,

   You need to install a "floating" neutral bar in the old panel.  This neutral bar is called a floating bus, in that it is not electrically connected to the panel housing (i.e., not bonded to the panel).  Basically it's a terminal bar that's mounted to a plastic spacer that in turn is screwed to the panel, with no connection 'tween the bus and the can.  You'll probably have to drill and tap a couple of holes in the can for the spacer (standoff) screws; most new panels have these holes already drilled a tapped.

   Then of course you 'll have to transfer all the neutrals to this floating neutral bar.  If things go the way they go, you might be better iff replacing the existing grounding bus with the floating neutral bus, then relocating the grounding bus.  Otherwise it's a lot of splicing to extend the neutrals.

   Don't forget to get an adapter terminal (or lug) that's big enough for the feeder neutral.  The lug is designed to take a big conductor (#1 or 1/0) and itself fit into one of the holes in the neutral terminal bar (which max out at #4).

   Ditto on the lug for the grounding bus.  And if you use aluminum feeders, don't forget the anti-oxidant grease (NOALOX or Burndy Penetrox-B.

   Good luck, you're asking the right questions to do a safe install.

   Cliff

1. 
   ahneedhelp | Jul 18, 2002 05:15pm | #4

   Cliff -

   You are helping me make this a very thorough learning experience.

   The neutral bus bar, as it appears in the old box, is not floating.

   I will have to do another thorough exam to make sure.

   This panel, with pushbotton breakers, is from the 1950s.

   With no separate ground bus bar, can it be assumed that the neutral is bonded to the panel enclosure ?

   I was amazed to find replacement breakers at our local supply house, which is where I am getting all the QO stuff.

   I will carefully digest what it is you said and make sure I have all the P's and Q's in order. Most of it makes perfect sense.

   I can also consult with the inspector to make sure things are kosher with her.

   At the moment, more urgent matter is charting a course through the walls with minimal disturbance to the plaster works.

   I have some new toys - a Makita grinder with diamond blade, a set of fiberglass rods that can be assembled up to a 24' length, and still need to pick up one of the wirenut twisters mentioned in my other thread on "push-in connectors".

   Take care !

   Alan

1. 
   toddlen1875 | Jul 19, 2002 03:49am | #5

   sounds like a pushmatic panel.  where is it in the house.  i would strongly consider using it as a junction box .  then you would pull several 12 or 14 thhn wires throug a conduit instead of three number 2 s plus a ground .  finding a isolated bus bar for that panel will be a pain ,  almost as big of a pain as fighting all of the feeder wires into that small of a box.  how many circuits are in the old panel?  i"ve never been happy with how those add on lugs that fit into the small holes to create a big one work.  thumbs and index fingers work for the wirenuts pretty good.  i strongly suggest 3m ranger scotchlocks.

2. 
   ahneedhelp | Jul 19, 2002 06:33am | #6

   Hi, Todd -

   The Pushmatic panel is in the kitchen out in the open, flush mounted just above a phone alcove.

   The junction box scheme has been suggested.

   Not sure if I fully understand.

   Eliminate all the breakers and splice each circuit to homerun wires to the new panel ? I guess that's the general idea.

   It could end up being the simpler solution.

   Please let me know if I'm off base.

   Thanks !

   Alan

3. 
   toddlen1875 | Jul 26, 2002 11:21pm | #7

    i think you got the general idea.  with the major appliances removed from the old panel into the new there shouldn't be to many circuits to fish in.  if there all lighting circuits( receptacles in bedrooms, living room Are also considered lighting circuits)  you can pull 14-3 to the box.  But  the part " over a phone alcove" sounds scary. is there attic above

4. 
   ahneedhelp | Jul 27, 2002 02:18am | #8

   Todd (and Cliff also)

   Thanks for posting the notes.

   Here's the current situation.

   Further investigation reveals....

   The two neutral bus bars, on either side, are indeed "floating" on a gray plastic looking base.

   The two neutral bars are connected via a copper bar that is wrapped in some sort of electrical tape looking material.

   Assuming I can trust this wrapping, there is nothing in the neutral that is touching the panel.

   This means I can add a ground bar to the panel and not float it.

   Simply attach it stright to the box metal.

   This is if I go with the sub-panel route.

   If I do the junction box, what would I do with the ground on the new wires running to the new panel ?

   The old wiring in the old panel are two-wire with no ground.

   Attach them to a new (bonded) ground bus bar in the old panel ?

   The P's and Q's are beginning to line up.

   Alan

5. 
   toddlen1875 | Jul 28, 2002 06:41pm | #9

   make sure there isn't a screw going all the way through the neutral bar to the panel.  if there is remove it for a sub and like you said just add one to the panel itself for the new ground.  if all the circuits are only 2 wire circuits(no ground) all you will need is a number 8 lug. because you will only have one wire going to it.  if you turn it into a j box just you could either istall a small bar for the individual wires or just wrap them up together under one larger lug.

6. 
   ahneedhelp | Jul 28, 2002 07:26pm | #10

   Hi, Todd -

   Thanks again for staying with me on this.

   The neutral bars seem to be mounted on plastic looking bases.

   Not good to assume too much but the plastic bases are mounted on the panel. Then the neutrals are mounted to the bases.

   At this point I can only guess that the neutrals are floating.

   Anyway, I will proceed cautiously because I am going to have to keep many of the wires in the old panel. Most of them are headed to the lower level and everything travels through finished plaster ceilings.

   My priority is for the main floor first, most of which can be accessed through the attic and lot easier to tackle first.

   A major load will be removed from the old, which includes the kitchen, bath, and BR, LR, garage outlet circuits.

   And yes, I am still considering the junction box route.

   Thanks for the lug suggestion.

   I'll report back periodically.

   I don't expect any of this to be a problem with the inspector.

   Alan