Trying to determine if upgrade to 200 amp service is needed. Is my approach correct?

[dustin wassner]

I turned everything in my house on to see what my total amps is. I used a clamp meter in the panel where the main enters. My service is 100 amps. My bandsaw has the biggest motor and I only use one tool at a time so this is what I had running during the test, but it was not under load.

Hot wire 1: 53 amps
Hot wire 2: 40 amps
Neutral wire: 8 amps
I did not check ground...

1st question: do I add 53 and 40 to arrive at 93 of my 100 amps available, or is it 100 per hot wire?

2nd question: is it normal to have each of the hot wires out of balance so much?

3rd question: is it normal to have an amperage reading at all on the neutral wire? I was expecting to see zero.

any input is appreciated

[Curt Harms]

Not a sparky and haven't played one on TV but I think that'd be considered 53 amps. If you checked voltage to ground each side would likely be around 120 volts. 120 volts + 120 volts = 240 volts. You have more 120 volt stuff on one leg (53 amps) than you do on the other (40 amps) so the neutral wire has a load. If all loads were 240 volt or perfectly balanced the neutral would be at zero. That's my understanding of it anyway.

[Mike Henderson]

Yep, it's 100 amps on the outside (hot) wires of the 240V circuit coming into your house.

The reason your two hot wires do not balance is that you must have had 120V circuits in operation when you did the measurements.

120V circuits will give you current on the "neutral" wire unless the 120V circuits are exactly"balanced on both hots. That is, if you have a 120V circuit on one hot drawing 10 amps, and a 120V circuit on the other hot drawing 4 amps, the current in the neutral will be 6 amps.

Mike

[The amps should add up - in fact, they have to add up - but I imagine you measured them one at a time so they could change between measurements, and your measuring device is probably not all that accurate.]

[Eric D Matson]

You will also have inrush current when starting anything really. Bandsaw, Air conditioner, refrigerator, etc. I would say you are fine for now. If you increase your loads in the future you may need to upgrade. I'm assuming you have gas heat?

[dustin wassner]

So I am at roughly 53 of my 100 available amps? Amperage on the neutral now makes sense...

we have natural gas heat/hot water/dryer/stove.

I have read that 80% the service rating is what should be considered the high end before upgrading, so it appears I can still take on 27 amps before needing to upgrade?

thanks again,
DW

[Mike Henderson]

So I am at roughly 53 of my 100 available amps? Amperage on the neutral now makes sense...

we have natural gas heat/hot water/dryer/stove.

I have read that 80% the service rating is what should be considered the high end before upgrading, so it appears I can still take on 27 amps before needing to upgrade?

thanks again,
DW

This is just me, but I'd wait until the main breaker tripped before I'd upgrade the service. You're only going to trip it (the first time) when you have an unusual amount of draw. Once you experience that, start planning on how to upgrade the service - and figure the cost.

Mike
[Of course, if you're doing some major remodeling, I'd upgrade the service as part of the remodel.]

[Wayne Cannon]

You only need capacity to run the things that are going to be running SIMULTANEOUSLY, plus some overhead for one item's starting current. For example: refrigerator, freezer, electric dryer, electric range, and table saw might all be running simultaneously; however, in a one person shop, you are unlikely to run more than one of a table saw, planer, chop saw, or bandsaw at a time. Pick the one with the heaviest draw and forget the others. If you invite the scout troop over and run multiple machines simultaneously, that's a different story.

You got good info regarding neutral current. If loads were all resistive (like light bulbs and heating coils), the neutral current would be the difference between the draw on the two legs; however, motors are reactive loads and don't simply add up nicely like that.

It's also unlikely that your freezer, refrigerator, dryer, oven, all cooktop burners (assuming an all-electric house) and table saw would all be on at tree same instant, but it COULD happen. You have to decide whether you want to take the risk and occasionally/rarely flip a breaker, or want that warm fuzzy guarantee.

[Wayne Cannon]

As a point of reference, I have never tripped a breaker in 24 years with my 100 amp service with freezer, refrigerator, electric dryer, 5 hp dust collector and 3 hp table saw (I have gas oven and cooktop). The dust collector and table saw are 240 V, which have half the current draw of 120 V units.

[Bill Dufour]

Were the air conditioning and air compressor running?
Bill

[Jim Andrew]

I would install a 200 amp service if I were building a new shop. However, my present shop has a 100 amp service, and I run a 3hp dust collector, an air compressor, and AC, a lot of lights, and a shop refrigerator along with what machines running at the same time, no problem.

[Wayne Cannon]

What Jim said.

I forgot to mention that my shop also has a heat pump and medium-size air compressor, plus the house's A/C and spa pumps on that 100 amp service with no problems.

I also agree with Mike's comment, paraphrased, that if you aren't encountering tripped breakers now and then, your service is ample.

There is one additional factor to consider -- voltage drop. You can measure the voltage at your service entrance during the starting of a large tool. You can also tell if your tools are occasionally sluggish starting, laboring noticeably (when there are already heavy loads). I'm an electrical engineer, but I don't know how much drop is too much, but would guess a drop below 100 volts for a 120 V nominal service would make me start to think about adding more capacity.

[Matt Marsh]

http://iaeimagazine.org/magazine/201...ectrical-code/

Residential service sizes are not calculated by simply adding up loads. If that were so, services would be much larger than needed. Demand factors and certain deductions are allowed to calculate service and feeder sizes adequate to supply the loads. Here is an example of how service sizes are calculated.

[Mike Henderson]

http://iaeimagazine.org/magazine/201...ectrical-code/

Residential service sizes are not calculated by simply adding up loads. If that were so, services would be much larger than needed. Demand factors and certain deductions are allowed to calculate service and feeder sizes adequate to supply the loads. Here is an example of how service sizes are calculated.

Wow, that's mind boggling. It'd take me a week to figure out everything in that article. What I got from a quick reading is that the calculations take into account that not everything will be turned on at the same time, and that the feeder wires can be rated for less than the service amount. So for 200 amp service, the feeder wires can be rated for a bit less than 200 amps.

Mike

[Anthony Whitesell]

A few years back I upgraded the service and main panel in my house from 100A to 200A. The main reason...more slots. The second reason was fear (perhaps nervousness is more correct).

I was concerned about the automatic heavy loads coming on simultaneously while I was using the tools. If I was using the jointer, power feeder, and dust collector and then the wife started dinner and the dishes, then the oven, well pump, and possible the fridge and A/C may come on an overlap. Just using breaker sizes as a ballpark reference, that is 20A 240V, 20A 120V, 20A 240V, 50A 240V, 20A 240V, 15A 120V, and 20A 120V. Plus the dehumidifer in the basement and the air compressor, another 15A 120A and 20A 240V. Just adding the breakers is 160A 240V. Since the breakers are sized for the startup, then estimate half that for running so 80A 240V. I haven't included any computers, other electronics, or lights (which must be on in the shop) that may be on.

As you can see, nervous. But the fact is, the panel was full. For me it was a two-for-one. I could add a subpanel, but why add a sub when I could do the upgrade for little more than the same price (although twice the time).

[Matt Marsh]

Mike,

There are Non-coincidental loads (e.g. heating and cooling appliances), where only the larger of the two loads are used in the calculation. It is also assumed that everything will not run at the same time, nor will everything be drawing full load at any one given time.