I’m a refugee from the FWW “Knots” forum but I have a two questions about home wiring that I’m hoping some of you can help me with.
The home in question is a townhouse built in SoCal in 1984. It has provisions for an electric dryer, with a NEMA 10-30 receptacle installed. That circuit has two 30-amp circuit breakers ganged together in the electrical panel.
Am I right in assuming that this is a 30-amp circuit?
The manual for the Delta 5-HP, 220V/1PH saws says they need a circuit that is “not less than #10 wire and protected with a 40-amp time lag fuse.”
Am I right in assuming that the dryer circuit described above is *not* adequate for that motor? Further, can I assume that it would be really dumb to even TRY to use that circuit for that motor, because the motor would blow the breaker during startup?
Am I right in assuming that this can’t be fixed by just substituting a higher-current breaker, but instead I’ll have to run either new wire to the existing receptacle location or install a new circuit for the saw? I can’t tell what gage of wire is currently installed, but I assume that whatever is customary for a 30-Amp dryer circuit won’t be large enough for a 40-amp breaker.
How do I determine if it is possible to add that new 40-amp circuit to the existing panel? This is a townhouse, and the meter is on the opposite side of the building with 4 other units between me and the meter. The existing panel has four 15-amp breakers, four 20-amp breakers, the two 30-amp ganged breakers for the dryer and two 20-amp ganged breakers for the stove/range. I’m guessing that they didn’t provide for much electrical panel expansion.
The label on the panel says it is limited to 125 amp max, but that is considerably less than the sum of the breakers already installed. So I’m not sure how I determine whether there is “room” to expand in that panel. There is lots of physical space but
Forgive the long ramble but I hope you see where I am headed. If I can provide a circuit for the saw without having to add a subpanel or mess with the wiring between my panel and the meter, it is doable. But if I have to live within the existing circuit limits then I’ll have to turn down the great deal I’ve found for a 5-HP saw.
Thanks!
Replies
It *MAY* work fine. You won't know until you try. Also, if the load (type of wood and how deep a cut, etc.) is light it should work fine. As you cut deeper and harder woods that stall the saw, breaker tripping may become an issue. But unloaded, the saw should start right up with out tripping the breaker.
You could possibly replace the 30 amp breaker with a 40 amp breaker feeding new 8 gage wire to a new receptacle for the saw. I don't know how practical this is for your home, pulling wire and cutting sheetrock, etc. The easiest would be to add a box under the panel with 8 gage wire to the replaced 40 amp breaker, and then use an 8 gage extension cord to feed the saw location. Not an OSHA approved method....
Frank DuVal
That'a a lot of questions. 1st, and mainly, for a circuit serving a single motor, the Code allows the breaker to be larger than normal for the wire size so that it won't trip when the motor starts. So, 10-gauge wire fused at 40a is acceptable in this case. (You can look at Table 430.52 at the end of Article 430 if you want to see it for yourself).
So you want to remove the dryer breaker and upsize it? Sounds like a plan to me. Likely the dryer circuit, if it's copper, is #10 since that's what code wants.
I would be surprised if your service couldn't handle the load, it's not a whole lot more than the dryer. What size is the main breaker? 100a?
Please don't tell us that your panel is FPE (Federal Pacific).
Ed
You're mostly correct. But as Frankie D suggests the motor MAY start and run find, and only trip the breaker if you overload it.
Re the panel limits, it likely has 125A main breakers. This means that the max current that can be drawn (ignoring code-mandated "safety margins") is 125A at 240V or 250A at 120V.
When you add up the individual breaker values, one problem you have is that you're adding the 120V breakers as if they were 240V breakers. A 120V breaker only accounts for half as much current as a 240V (two pole) breaker with the same current rating.
Further, "overloading" is permitted when its reasonable to believe that not all loads will be at max at once. Most lighting circuits, for instance, only draw a few amps, even though the breakers are 15-20 amps.
To determine if there is "room" in the panel, add together the 240V loads that are likely to be on simultaneously -- eg, range plus air conditioner plus water heater. Then take a "SWAG" at the load from other circuits -- eg, maybe figure two dozen 100W light bulbs, plus an eqivalent amount for TV, computers, etc, say, or about 5000 watts ==> a hair over 20 amps at 240V. Subtract the total of all of these from 125A and find out how much is left.
Dan & Ed-
Thank you for your thoughtful replies. I really appreciate it.
Thanks for the tutorial on circuit breaker algebra. If I understand you correctly, the "face value" of the 120V breakers is 140A @ 120V, which becomes 70A at 240V. Add the 50A of 220V breakers, and that gets us to 120A. The Panel appears to be a 125A panel, so there doesn't appear to be a lot of "headroom" unless some of those loads can be discounted.
And the main breaker is only 100A which doesn't help.
Time to call a pro to see what is really feasible and what isn't. If I can either upgrade the existing circuit or add a new one to the existing panel, that is doable. If I have to upgrade the main breaker, that is probably beyond where I'm willing to go.
If my existing 110V saw is any indication, the peak load is likely to occur during start, so I don't think it would be feasible to try and run it off the undersized breaker.
Thanks again for your thoughts.
-Tom H.Ventura, CA
BTW the panel is a Sylvania AL12(8-16)C type 1 enclosure rated at 125amps max.
As I said, many of those loads can be discounted. It's perfectly "legal" to "overload" a breaker panel with more breakers than the panel/main breaker ratings. You basically just need a convincing argument that they'll never all be drawing full power at once.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
The load that occurs during motor startup is very short. Most breakers are designed to withstand a short overload to accommodate motor startup. The worst-case load (outside of a true overload) is when you're sawing something thick/heavy and feeding very rapidly, causing the motor to slow down to half speed or lower.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Hendo,
The face value sum of your circuit breakers really doesn't mean much.
The issue, as Dan says, is the actual load on the panel. There is a method of determining the load on a service, outlined in the NEC, and an electrician should be able to do it for you. It's based on square footage of your home and consideration mostly of any motors/compressors and heat-producing electric appliances (oven, water-heater, dryer, electric heat).
An underlying aspect of the service calc is what's referred to as "load diversity". This is the reality that the various loads in a house are 1) not all used simultaneously 2) even when on, cycle on and off regularly (an oven heating element for example, cycles off and on when baking).
As I said, I'd be surprised if your house couldn't accomodate the 5 HP motor, especially with the dryer out of commission.
Ed
Here is the chart for calculating electrical requirments.
http://www.taunton.com/finehomebuilding/how-to/articles/sizing-electrical-service.aspx
Use NAMEPLATE DATA and not breaker size for all of the appliances except where they tell you to use circuit size or a fixed number.
But you can't do it.
One important thing that everyone is ignoring.
YOU DO NOT HAVE AN EGC (ie, ground wire).
10-30 R is 2 hots and a NEUTRAL.
However, that being a townhouse there should be a disconnect by the meter and your panel is a sub-panel and it should be wired with a 4 wire dryer circuit (14-30R).
But it is possible that it was wired correctly and at some point someone had a dryer with a 10-30P cordset and changed the receptable rahter than converting the dryer.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yeah, Bill is correct that you should check out the ground/neutral connection. Your motor circuit receptacle should be wired 2 hots and a ground.
You've got to have one or both in your existing circuit so it should just be a matter of hooking things up right.
Ed
Even if it is only a 3-wire cable, it should be a simple matter of switching the neutral wire to the ground bus in the panel, with appropriate labeling (green tape on the white wire on both ends, eg).
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
You can, but code only allows remarking grounds and neutrals for larger wires sizes (#2 or larger, but I might not have that right)..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I do not recall a code rule for remarking wires with different colors only for a given size. In house wiring we remark 14 and 12 ga all the time when wiring 3 way switches, typically changing neutral color to hot color. A sharpie works great for changing white to red or black. Also changing white to red for 240 volt equipment that doesn't require a neutral.I use tape or heatshrink to mark as ground in conduit runs with wire as small as #8. But that is just me as I typically have green 10,12 and 14 THHN.Frank DuVal
The restriction is on remarking to make it a grounded conductor or EGC.200.6(A) Says that grounded conductors 6 AWG or smaller have to white, gray, or 3 white strips. With a few exceptions such as the rib on lamp cord.200.6(B) says that larger than #6 you can remark it at installation with white or gray.250.119 says that the EGC can be bare or green or green with yellow strips and can never to used for a grounded and ungrounded conductor and can't be remarked.250.119(A) say that insulated conductors larger than #6 can be remarked at installation to an EGC.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I guess I will have to buy a roll of #8 green!Frank DuVal
Thanks for all your responses -- they are very helpful.
I removed the cover plate and pulled the dryer receptacle away from the wall. There is an unused fourth wire coming into the box so I'm hoping that is a four-wire circuit that was wired into the 10-30 receptacle.
So I'll take this opportunity to convert the dryer to 4-wire plugs.
Thanks again for your help.
-Tom H.