What size of sub panel do I need?

Reply

  #1  
Old 01-23-17, 08:58 AM
Member
Thread Starter
Join Date: Jul 2016
Location: Canada
Posts: 30
Received 0 Votes on 0 Posts
What size of sub panel do I need?

Hi all,

I have a question regarding electrical panels.

I am currently building a secondary dwelling unit (SDU) in the basement of my house. I am thinking of putting all SDU circuits on a separate subpanel in the basement, for the following three reasons; 1) there is not enough space in my current panel to supply all circuits downstairs and upstairs the panel is a 24 circuit for single pole barkers; 2) I would like to separate the circuits, so each my tenants have access to their own panel in case something trips and I will have control of all of own electrical upstairs; 3) possibility of sub metering the electrical in the future.

In terms of the major appliances load, I will have two ranges, two dryers, 2 washers, 1.5 ton AC unit, 2 microwaves, 2 fridges. Heating is gas. My current service is 100 AMP. The first thing I did is perform the load calculation, and taking into account all lighting, appliances and plugs, I come down to 93 AMPS.

Now, an electrician suggested that I should get a 60AMP subpanel so supply all the load in the basement, but I am not sure whether the 60 AMP will be enough to supply all the load in the SDU taking into account the fact that the range itself requires 50AMP breaker and the dryer 30Amp, this is not counting any plugs or lights. Does this alone mean that a 60 Amp sub panel would be inadequate to serve the loads in the SDU?

Attached is my electrical plan of the SDU, please feel free to make any suggestions and/or comments.

Thank you!
 
Attached Images  
Sponsored Links
  #2  
Old 01-23-17, 10:51 AM
Member
Join Date: Oct 2008
Posts: 1,312
Received 0 Votes on 0 Posts
I would install a 100 amp subpanel minimum and plenty of extra slots.

Panels are quite inexpensive. More slots (spare) not much more cost. However breakers are expensive and larger gauge wire can cost a small fortune.

But replacing the subpanel later would cost even more. So give yourself some extra amperage and extra empty slots for the future!
 
  #3  
Old 01-23-17, 11:45 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
I think the 60A panel would probably be just fine; however a 100A will not cost too much more if you want to go that way. Where is your home's main panel in relation to where you would like to install the secondary panel?
 
  #4  
Old 01-23-17, 12:25 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,493
Received 33 Votes on 25 Posts
3) possibility of sub metering the electrical in the future.
If the sub-metering proposed is to recover the cost of electricity rather than purely informational you need to be aware of the rules regarding such a practice. Many utilities frown upon sub-metering and there will be state laws concerning the allowable equipment and procedures.

Far better, in my opinion, is to install the sub-panel along with some conduit that will allow for a second service from the utility. This could terminate near the existing service and then a J-box with conductors back to the original service panel until (if ever) you decide to have the tenants responsible for their electrical usage. Of course the new (sub) panel will have to meet the minimum requirements for a service panel, usually 100 amperes, and be listed for use as service equipment.
 
  #5  
Old 01-23-17, 01:29 PM
Member
Thread Starter
Join Date: Jul 2016
Location: Canada
Posts: 30
Received 0 Votes on 0 Posts
ibpooks and Bill190,

Thanks for your suggestions. I am yet to find a 100 AMP subpanel, but I was wondering if it is possible to get another 100 AMP panel, which has the main breaker on it, and wire it off the original panel by putting in a 100AMP breaker in the Original panel? Also, do you think the 100 AMP service is enough to supply what I am proposing to do?

To answer your question, the subpanel would be around 2-3 feet away from the existing panel.

Thanks
 
  #6  
Old 01-23-17, 01:35 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
The panel needs to have at least the rating of the feeding breaker. For example, you can feed a 125A panel with a 100A breaker.

A main breaker is not required for a subpanel in the same building as the main. You can use a main lugs only MLO panel.
 
  #7  
Old 01-23-17, 02:40 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
I am yet to find a 100 AMP subpane
That is because that is just a slang term for any panel after the first breaker or fuse. The term doesn't exist in the NEC. Any 100 amp panel will work but you will usually have to buy a ground bar and add it to the panel. If you may eventually add a meter for a second drop then it should be a main breaker panel now. Another advantage to a main breaker panel is you often can get a main breaker kit which includes the panel, main breaker, and some common branch circuit breakers cheaper than a main lug panel with no included breakers.
 
  #8  
Old 01-23-17, 05:00 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,966
Received 59 Votes on 52 Posts
Many utilities frown upon sub-metering and there will be state laws concerning the allowable equipment and procedures.
We do work for many commercial customers who use sub meters to meter all sorts of larger electric loads. None of these involve the power company and they are all installed indoors and read by the landlord. The usage is then back charged to the tenant as allowed in the lease. Most cases we install Emon-Dmon or Leviton sub meters.

The only issue I can see is the added load to your existing service. I recommend doing a load calculation to make sure your existing 100 amp service can handle the new load(s).
 
  #9  
Old 01-24-17, 07:46 AM
Member
Thread Starter
Join Date: Jul 2016
Location: Canada
Posts: 30
Received 0 Votes on 0 Posts
Once again, thank you for all of your suggestions guys.

So what I gather from all of this is that I can install another 100AMP panel with the master breaker on it and feed it with a 100amp breaker from my existing panel?

Would anyone be able to recommend a good resource tool for calculating load?

Thank you.
 
  #10  
Old 01-24-17, 08:25 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
If you search Google for "demand load calculation" you'll find some spreadsheets or other online guides to work through the calculation. This exact process is based on the US code, but CEC should be pretty close.
 
  #11  
Old 01-24-17, 10:11 AM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: