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Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3723
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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I actually have 2 questions a detached working shop. I plan

Customer Question

I actually have 2 questions for wiring a detached wood working shop. I plan to have 10 outlets. 1 for a small fridge and window a/c, 1 for a 2nd dust collector and 1 for a air filter. Rest for various tools. I'll also have 2 fluorescent lights in the shop. I have room in my main panel for a 50 amp feeder breaker and plan to run 6/3 uf from main to subpanel and wire with 10/2 for the circuits. So my questions are .. 1 is my pLan so far good and what size main breaker can I put in the sub panel?
Submitted: 2 years ago.
Category: Electrical
Expert:  Kevin replied 2 years ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) What is the approximate distance from the main panel out to the wood shop sub-panel location? I need to calculate the voltage drop.

2) Do you have the amp draw or the watts for the dust collector and air filter?

3) Will any of the tools or A/C unit be 240 volt circuits or all will be 120 volt?

Customer: replied 2 years ago.
Roughly 100 feet dust collector looks like 12 amp at 120 and 6 at 240 filter specifies 15 amp minimum circuit. All my equipment runs 120 currently in the garage. Just a 1 man shop so never really any need for more than one tool running at the same time. Filter and dust collector won't alway run at same time either
Expert:  Kevin replied 2 years ago.

OK, very good........Thanks for the replies.

Check back here in around 20 minutes or so as I need to calculate and provide you with a write-up for the answers............Thanks............Kevin!

Customer: replied 2 years ago.
OK I guess while I'm at it can you tell me if I should have separate circuits from outlets and the ac/fridge, dust collector and filter?
Expert:  Kevin replied 2 years ago.

1) National Electrical Code recommends that the voltage drop be 3% or less. Using a 100 foot feeder circuit @ 240 volts and at 60 amps, this results in using 6 AWG Copper for the sub-panel feeder circuit. Voltage drop on 6 AWG copper will be 2.4% or a loss of 5.7 volts. Therefore, code compliant for 6 AWG copper.

2) Yes, you can install 6/3 Underground Feeder with a bare copper equipment grounding conductor. The UF cable needs to be buried a minimum of 24" below final grade. Personally, I recommend to install Sch. 80 gray electrical PVC conduit as UF cable can fail over time due to shifting soil conditions as rock heaving, punctures, etc. A minimum of 1" Sch. 80 gray electrical PVC would be required using a quantity of (3) three 6 AWG Copper conductors rated as insulated type "THWN" and (1) one 10 AWG Copper, type "THWN" for the equipment grounding conductor. All sub-panels require a 4 wire feeder circuit comprised of 2 hots, 1 neutral and 1 equipment ground. Sch. 80 PVC conduit needs to be installed a minimum of 18" below final grade. Therefore, less digging/trenching using PVC conduit as compared to UF direct burial cable:)

3) Since a detached building you will need two 8 foot ground rods installed at the outbuilding spaced a minimum of 6 feet apart. Use 8 AWG Copper for the ground rod conductor to the sub-panel. The grounding electrode conductor (8 AWG copper) will terminate to a separate equipment ground bar at the sub-panel and NOT to the neutral bus bar.

4) I recommend installing a 60 amp double pole breaker at the main panel for the feeder circuit and purchase a main breaker panel to act as the sub-panel. The main breaker in the sub needs to be a minimum of 60 amps. 6 AWG copper will support a maximum of 60 amps.

5) I recommend the following branch circuits at the sub-panel:

A) Dedicated 20 amp/120V for the A/C unit

B) Dedicated 15 amp/120V for the lighting

C) Dedicated 15 amp/240V for the filter

D) Dedicated 20 amp/120V for the Dust Collector

E) Dedicated 20 amp/120V for the remainder of receptacles

All 120V receptacles need to be GFCI protected.

6) At the sub-panel, DO NOT install the green main bonding screw or a main bonding jumper strap. On all sub-panels, the neutral must remain isolated from the panel metal enclosure. Only land white neutrals to the neutral bus bar and never any bare copper grounds on the neutral bus bar. All copper grounds will land on a separate equipment ground bar that you must purchase separately.

7) For the 100 foot run, I recommend to install a "Warning Ribbon" tape approximately 6" below final grade above the entire trench. The warning ribbon tape will provide a warning to anyone digging above the run that an electrical line exists below that.

8) The 20 amp branch circuits will require 12 AWG copper and the 15 amp circuits can use either 14 or 12 AWG copper conductors, type THHN rated.

10 AWG Copper is not required for the branch circuits.

Hope this helps………If you have any additional questions, let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

The next time you have an electrical question, you can also request for me at: ……….Thanks…………..Kevin!

Customer: replied 2 years ago.
Thank you!
I think I have new questions now.
I think I only have room for a 50 amp feed in the main. How can I check if a 60 amp will work?How do I connect the ground to the grounding rods and I'm assuming that goes below grade as well along with the rods being driven down into grade.Just to make sure the uf 6/3 that has the 4 lines does suffice and if I put in conduit it's only 18 inches below grade correct?
Expert:  Kevin replied 2 years ago.

1) The best way to check is to fire up all possible loads in the main panel. Turn every light, TV's, radios, electrical appliance, central air, etc. to the ON position in the home. Then measure the amps on each of the 2 hot phases at the main breaker and subtract the total service amps from the measurement. The difference will be a good indication as to the maximum amps you have remaining.

For example, if your main service is a 200 amp and you measure 120 amps on one leg and 130 amps on the other leg, you have approximately 70 or 80 amps to spare for the sub-panel feeder breaker.

2) The ground rods are pounded into the soil at the exterior of the out building. All 8 feet are required to be below final grade. You will need 2 ground clamps for the rods. Start at 1 rod and then run a contiguous 8 AWG bare copper ground wire to the next rod and then from the 2nd rod back to the separate equipment ground bar in the sub-panel. No splices allowed on the grounding electrode conductor. 1 conductor only here.

3) Don't install UF inside conduit unless you increase the pipe diameter to a minimum of 1 1/2" or 2" . Pulling UF cable thru pipe will be a challenge due to the exterior insulation. UF cable contains 1 exterior and is difficult to pull especially on a 100 foot run, unlike 4 separate wires. Much easier to install 4 separate "THWN" conductors in the conduit:)

Customer: replied 2 years ago.
Thanks again.
I only have a 30 foot span from house to shop the rest of the run is attic space from main to closest point to shop so look like 40 or so feet of conduit from house to shed to go below grade across and back up.
Expert:  Kevin replied 2 years ago.

No problem, glad to assist.

Very good as a 40 foot run is much easier to dig and trench than a 100 foot run:)

If you have any additional questions, let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

The next time you have an electrical question, you can also request for me at: ……….Thanks…………..Kevin!

Expert:  Kevin replied 2 years ago.

If you have any additional questions, let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.