Converting 50amp receptable to 20amp for table saw/jointer

[Duncan Whitney]

Hi,

Moved into a new home that has several 50A breakers and 10-50R receptacles run in the shop area (and supporting heavy gauge wiring..). I need to convert them over to 20A/5-20R receptacles to use with my shop tools (unisaw, 8" powermatic jointer etc. that have 5-20P plugs on them already).

Wondering if I need to replace the 50A breakers for 20A breakers in addition to replacing the receptacles themselves (I'm assuming this is a definite yes... and probably scares the crap out of anyone who knows the right answer but since I don't for sure... :) ).

Anything else I need to consider in this instance I'm overlooking?

Thanks

[Chris Friesen]

You've got a few options.

1) Replace the receptacles and the breakers to match the plugs on the tools.

2) Replace the plugs on the tools to match the breakers.

3) Make little pigtail extension cords with 50A male ends and 20A female ends.


If you do change the receptacles to match your existing plugs, you *must* then change the breakers to match the receptacles. (Otherwise if something went wrong the breaker would feed more power than the receptacle was rated for.)

Basically all heavy-duty woodworking equipment has overcurrent protection built in to the tool. This means that the breaker really only protects the wiring in the wall. Because of this, you can safely plug your tools into the existing circuits...you just need to match the connectors. Thus, options 2 or 3. There's no real difference--option 3 would let you get away with one adapter cable but you'd need to move it around. Option 2 would be the cheapest if you want to leave everything plugged in all the time.

[David G Baker]

I would install a 50 amp sub panel in place of one of the 50 amp receptacles if the right number of wires are available and put the number of 20 amp breakers in the sub panel that I need circuits for then run the appropriate sized wire to the 20 amp receptacles for the equipment you want to power.

[Chip Lindley]

Just make some adapters of a short length of 10-3 cord, with 50A male plugs on one end, and female 5-20 on the other. Make them longer, and call them extension cords to reach different machines easily.

Just as soon as you change out your 50A receptacles, you will acquire a big welder and a big air compressor, and need to change them back again.

[Mike Black Milford, MI]

Ditto on what David G. Baker said.

[Britt Lifsey]

Ditto on what David G. Baker said.

+2. Not an electrician but agree...make use of those extra amps ;)

[Foras Noir]

Breakers only protect the wire and other in-wall parts. They do not - ever - protect equipment. That is simply a design and code axiom. Don't even try to talk around it.

If you have xxx A breakers protecting xxx A in-wall parts you are fine.

A cheap solution is a "job-site box." It typically plugs into (lucky in this case) 50 A circuits. It breaks them out to smaller lumps of power. Check out CCI X-Treme as one example. I - 4 times now - have taken a CCI part no. 019703R02 and replaced the L6-30R (30 A 3 wire) to an L14-30R (30 A 4 wire) plug. Then I can use cords to separate out whatever I need in 220V. Cheaper than a sub-panel and you don't need an electrician. Man - the diameter of the holes in the box fit the L14-30R exactly.

Simple stuff done cheap and legal wins over complicated folklore that takes you off to electrician land rather than woodworking.

[Adam Strong]

Breakers only protect the wire and other in-wall parts. They do not - ever - protect equipment. That is simply a design and code axiom. Don't even try to talk around it.


+1

You MUST either replace the breaker, or go the sub panel / job site box route. DO NOT put a smaller gauge wire pigtail in line to only adapt plugs. There is always the 50 amp potential as long as the breaker is a 50 amp, smaller wiring is a hazard even in pigtail form. A 50 amp surge will kill your 20 amp equipment, the investment required to do it right is much cheaper than doing it cheaply in the long run.

[Tom Godley]

If the number of converted 50 amp outlets will be sufficient then you can simply switch out the receptacle and change the breakers to match.

Do not use 50amp plugs on your tools or make up pigtails to allow plugging in a tool with a 20amp plug. A properly fused job-site box with the proper secondary fuses are safe -- but many are not. You do not want 20amp tools plugged into 50amp circuits.

The max circuit ratings on equipment is to protect you from installing them into a circuit with too high a rating.

[Wes Grass]

All that, and never mind the challenge of getting the 50A wiring into a 20A breaker and outlet.

[Tom Godley]

The "spec" grade leviton outlets should be no problem. They back-wire with a clamp and a screw and I am looking at a Square D breaker and the clamps for the 20 and 40 look the same (no 50 handy) -- I did this not that long ago with a dryer feed and did not have any issues. Other manufacturers designs may present problems.

[Duncan Whitney]

Great info guys. Appreciate all the ideas and quick response. Hope to return the favor some day.

Cheers.

[Van Huskey]

The max circuit ratings on equipment is to protect you from installing them into a circuit with too high a rating.

Where do you find the "max circuit rating" for a given piece of equipment? Every machine I have is listed with a MINIMUM circuit rating but never seen a maximum. I am just curious, if you have a 6 amp drill do you plug it into the, probably, 15 amp duplex outlet on a 20 amp breaker? Foras is correct breakers are NOT to protect what is plugged into a receptacle they are ONLY there to protect the in-wall wire and receptacles. Think about this the next time you plug in a laptop charger/adaptor pulling maybe 1.5 amps into a 20 amp circuit. Lets consider a real life woodworking example, the Grizzly GO555 draws 5 amps at 220V, the minimum circuit is listed at 10 amps (I bet 90+% of these wired for 220 are on 20A or more breakers). Even if the bandsaw is on a 10 amp circuit a motor with a draw of 5A is gonna be toast if it draws 9 amps for any time at all. I never understood why on 20 amp or lower circuits people think nothing of plugging in something with a current draw of 1/100th or less of the breakers trip amperage but plugging a 20 amp tool into a 50 amp circuit gives them nightmares.

Foras offers the least expensive/easiest solution and does not pay homage to the wives tales associated with this issue.

I do want to make one thing clear do NOT mis-match breaker and receptacle ampacity (wire is fine as long as the ampacity is higher) within the walls UNLESS allowed by code ie the 15 amp duplex receptacle on a 20 amp circuit, NEC article 210.21 (B).

[Tom Godley]

Van.

I have run into a lot of industrial equipment that lists max circuit protection -- although not many of my woodworking tools. I have noticed it listed in Grizzly equipment manuals and I was just doing some research on a European woodworking tool and I came across it.

This re-plugging subject has come up before.

The laptop charger you referenced is designed for a maximum current and the limiting factor is the installed plug. The whole product was designed around this intended circuit amp. You can not plug it into a circuit with a greater amp rating - In the USA we limit by plug type. Inadequate supply cords is a major factor of UL rejection. With a power tool supplied without a plug from the manufacturer -- you become the limiting factor -- because any plug at all can be installed.

Many countries throughout the world use only 220v's -- Many at 30amp. They limit the current past the plug by using fused plugs -- you do see this on a limited basis in the USA. The need for this is because the supply wires past the plug are designed for a maximum current as is ultimately whatever is being powered. I have no idea what a factory Unisaw supply cord is rated for -- but it is not 50A. If something happened at the switch of that tool - causing an over-current situation - the supply wires could easily melt and start a fire long before a 50amp breaker trips. With a mobile tool in a workshop the supply line could easily be 15' long.

Its the same as overloading an extension cord and why in many industrial situations they are not allowed --- along with any type of adapter or "job site box" as we are calling them on this thread. Over-current in supply cords is a very common reason for electrical fires and it happens all the time.

Having a homeowner using what is in effect a 50amp extension cord is IMO - not a good idea.

[Rod Sheridan]

Both of my Hammer machines have a recommended protection setting of 16 amperes, and a maximum circuit ampacity of 20 amperes.

It's important not to exceed the maximum values due to the design and rating of the electrical components in the machine.

Regards, Rod.

[Rollie Meyers]

If one tries to convert the circuit to 20A will run afoul of NEC article 250.122(B) because the equipment grounding conductor will be to small in a NM type cable. (6 & 8 AWG NM cable has a 10 AWG grounding conductor).

This is a copy & paste from the 2008 NEC. (Unchanged from 2005).

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.

Bold by me.

If the cable is 3-conductor W/ ground a small subpanel would be the ticket.

[Tom Godley]

Rollie: Can you explain this further -- I do not understand.

I converted a feed that once was used for an electric dryer - to run a 220v pump. Installed a 20amp breaker and did not use the neutral - Why would a 10awg ground conductor be a problem in this situation.

Thanks for the info!

[Hugh Jardon]

I suspect because under ground fault conditions, the ground conductor becomes the return path for the circuit. If the return path is not rated to carry the current that the live can provide, then it may fail, thus rendering the load live.

[Chip Lindley]

I cannot delete my previous post, so I will insert a disclaimer. What is simple and works, may violate some code, etc. Disregard my unprofessional and unsafe advice.

[Matt Meiser]

Could he put a fused disconnect in place of each 50A outlet with the appropriate fuses and the proper receptacle on the load side?

[Chip Lindley]

This thread has been all over the place, so, would be hard to hijack it.

To further basic understanding, and in the interest of safety, somebody please give me a scenario that could possibly occur to cause damage to motor, starter or wiring of, say...my 1.5hp 8.4a, 230v DJ20 jointer on a 50A circuit! The motor is double protected by a thermal reset and an overload heater in the magnetic starter.

The jointer is plugged into a 25ft. 8-3 extension cord with 6-50 male and female ends. A short 10-3 pigtail adapter has 6-50P to L6-30R. The jointer has an 8ft. 12-3 cord. You have the chance to fry my nice jointer, or burn down my garage. Go for it!

And...what would be different that would not happen with my Lincoln welder using the same 50A circuit which it specifically calls for??

[Rod Sheridan]

Hi Chip, I can't comment on your jointer beacause I don't have any of the "uncommon" information that all electrical components have.

This would be the withstand ratings of the devices, which esentially is how much current can they carry, or interrupt (turn off) without exploding or catching fire.

The circuit that feeds your jointer has a breaker or fuse, and a circuit impedance that limits the maximum short circuit current the circuit can deliver.

The maximum short circuit current is larger on higher ampacity circuits, so the internal components of machines meant to be connected to these circuits will have suitable withstand ratings for the expected maximum short circuit currents. (This means they are larger and more expensive).

Your welder would be just fine on a 50 ampere circuit, your jointer may, or may not be, only the manufacturer, or a complete evaluation by an Engineer can tell you that.

I have two machines that do list the maximum over current protection required, I also have machines that don't.

It's always good practise to reduce short circuit currents through the application of correct overcurrent protection, including in some cases the application of current limiting fuses.

Regards, Rod.

[Tom Godley]

Chip - The concern is not about the basic operation of the tool.

On a modern tool/ machine if the motor develops a short or becomes overloaded the combination of internal overload protection and the application of a thermal overload in the switch should protect against a fire. The same is true for the wires between the motor and the switch -- if the switch has protection built in.

The problem is from the switch to the outlet -- What protects this wire??
The only thing protecting this wire is the breaker in the panel - in your case this wire is almost 35' long. What happens if the switch develops a problem before the overload protection or does not have any overload protection? Or you drop a sharp tool on the wire and damage it in some way? You can have a short that develops and the breaker will allow a 50amp load to be placed on that supply line. Will the 12g section handle the load? How will the damaged area of the 8g extension handle the problem. The overloading of supply lines is a common cause of fires. Have you ever compared the single spark from touching a 15amp vs 20amp line together. Now think about a 50amp line and wood chips in a shop.

Nothing is gained by having 50 amps supply a tool that will run and was designed to run on 20amps.

[Matt Meiser]

So actually you could put a 2 circuit subpanel at each location dirt cheap (meaning about $15/location + breakers) With quadplex breakers you could even put both a 20A and 30A 220 circuit at each location giving you a lot of future flexibility.

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