Updating main breaker on electrical panel

[joebk]

Have some garage work going, and I am looking into adding two 20 amp lines into the garage.

I checked the main electrical panel, and the main breaker has 100A rated.

With the additional two 20amp circuit, I think I need to upgrade the 100A main breaker to a 200A main breaker.

I checked w/ utility and they're going to call me back to let me know if the main service power line into the house has enough capacity for my upgrade to 200A main.

In the meantime, I wonder for the main panel it's just the main breaker I need to update (to 200A main breaker), and it'd be ready for two new lines to the garage.

Or I'd actually need to swap out the electrical panel itself?
(Don't know if the two bus bars inside the existing panel have enough capacity for the additional power to flow thru')

 

[pattenp]

If the existing panel is 100A you need to replace the whole panel with a 200A panel to get 200A load capacity. You can add the two 20A circuits if the 100A panel has the space.

 

[Stuart in MN]

Adding two more breakers doesn't necessarily mean the panel will be overloaded. There are various calculators online that will help you figure out what the total load is, here's just one: http://www.electricalknowledge.com/SFDLoadCalc.asp

 

[joebk]

Current max total load won't go beyond 100A yet, as two high amp (one 30A and one 50A) circuits aren't used at the moment.

So for now, even after adding the two 20A circuits and turning all appliances (incl. the two new 20A circuits), the panel won't be overloaded.


The thing is, the total rated #Amps on each bus (based on sum of all rated Amps on all the breakers) will be > 100A once I add the two 20A circuits.

So if I do fully utilize all circuits to the max (although I don't right now), for sure the 100A main breaker will jump. As I might use the two unused high amp circuits in the future.


The electrical panel is basically comprised of circuit breakers and the two bus lines for the two hot wires from the service line (mine doesn't have any other fancy components), and then the ground/neutral buses.

If the existing panel is 100A you need to replace the whole panel with a 200A panel to get 200A load capacity.

Haven't compared a 200A panel to a 100A panel, so don't know if the main difference is just the main breaker, or heavier gauge bus lines also.


If a higher load capacity panel implies higher capacity bus lines, then I'd want to get a 200A panel eventually (won't be just switching out to a 200A main breaker on the 100A panel) even though this might just be a distant concern... .

 

[Charles (in GA)]

Its OK to have much more amps of breakers in a panel than the rating of the panel, all houses do, its because not everything is on at once, and breakers are designed to protect wires, they have to have the ratings they do for the wire connected to them, but rarely is there anywhere near the max load on a breaker.

As far as 100 amp vs 200 amp, it depends on what the panel is rated for. You will find out what is allowed in the panel if you look on the placard on the inside of the door, It should have all the specs and sizes and part numbers of main breakers, branch circuit breakers, accessory lug p/n's, etc.

You should certainly not size the main breaker any larger than the service entrance cable wires are rated to carry.

Charles

Charles

 

[joebk]

Thx for clarifying. Perhaps I don't need to worry about swapping out the panel yet right now as I won't be using that two high amp circuits now so there's no immediate concern of overload.


I'll chk on the specs on the panel if the parts are ok for 200A, although I recall seeing the spec on the panel has the wording '100A', etc. (not seeing specifics for each part however).


---

For my immediate work on the garage I guess I'd go ahead w/ adding the new wires.

Haven't looked into the details on how the wires branch out from the main panel into the house,

but it seems they all go downward -- into the crawl space? Don't know how the wiring goes from there and how some of the wires re-route back up to the attic for all the lighting on the ceiling in the house?


Also it seems contractors all added new wires for new circuits in the recent past thru' the crawl space instead of thru' the attic.


Perhaps it's easier to get a new wire down thru' the crawl space instead of pushing it up to the attic? Don't know if anyone knows the reason for the preference. I do see a 240v wire (for the electric dryer) going thru' the crawl space and into the garage thru' the gap along the water pipes.

 

[jvitez]

Don't worry about amps, worry about watts! Sort of...... Remember Ohms law V=IxR, or sing-song with me: watts over volts equals amps.

Add up the wattage, not amperage of everything you might have running at the same time off of that panel. Now divide by 240. Is it higher than 100? If not, no need to do anything but add your new circuits. If so, you'll need an appropriately up-sized main wire, and a 200 amp rated panel with a 200 amp main breaker.

A 100 amp feed is 100 amps x 240 volts = 24,000 watts. That's a lot of power! For example:

let's go crazy and say you have 50 2-lamp fluorescent light fixtures with 32 watt bulbs, roughly equal to 3200 watts. You're also running a 6500 watt welder, and your 5400 watt air compressor kicks on at the same time. Plus, you have two 1500 watt plug in heaters running, and a 1000 watts of Metalica pumping through your awesome garage sound system. What's you gots? 19.100 watt of power consumption, or 79.6 amps.

Add up the wattage of everything to do a proper load calc.

 

[wyliesdiesels]

Figuring out load capacity by adding breaker ratings is a common misconception and a newbie mistake. In the OPs situation, adding 2 20a circuits is not gonna cause any problems with his 100a panel. Very few circuits pull the max amperage rating of a breaker. For example, my package A/C unit is fed with a 40a breaker. But when I put a clamp meter on it, its only drawing about 23a. My range, also on a 40a breaker, pulls about 10a when I bake a pizza. My dryer is fed with a 30a breaker and it pulls about 20a! Don't add breaker amps!! In order to figure out actual load, u must do load calcs and stuart above has given u a link to a load calculator!

 

[rodm1]

Unless you have a good reason it would be a wast of money to upgrade to 200 amps. In your case I don't see one.

 

[joebk]

Thx for all the eager help! -- I figured that out when Charles (GA) responded.


Onto figuring out how to do the actual wiring,

I talked to a HD guy and he said that the wires going down from the main panel were probably rerouting back up to the attic somewhere for the lighting in the ceiling. To get two new wires into the attic I might need to break up the exterior stucco wall right above the main panel and drill hole to get the wires into the attic.

That seems a lot of work, so I'm opting to run the wires straight down from the panel (inside the stucco wall) and then run them along the crawl space underneath to the garage instead. Don't know if that's good enough.


Anyone has some good ideas to run the new wires into the garage? This is a single family house (single story).