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Steve G.
Steve G., Electrical Engineer
Category: Electrical
Satisfied Customers: 16908
Experience:  27 years in Electrical Engineering, designing electrical plans and specifications.
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Hello I have a 240v outlet and want to add a 120v outlet nearby.

Resolved Question:

Hello
I have a 240v outlet and want to add a 120v outlet nearby. I connected the new 120v outlet to one hot lead on the 240v outlet and also to the unused neutral in the 10/4 wire feeding the 240v outlet. When i put my tester in the new 120v outlet I get a reading of 146v!? Any ideas on why this would happen?
Submitted: 1 year ago.
Category: Electrical
Expert:  Alex replied 1 year ago.
Hello and Thank you for posting on www.justanswer.com. My name is XXXXX XXXXX I'm here to help you.

Is 240 outlet in use or you want to eliminate it?
Customer: replied 1 year ago.

It is in use and I would like to continue using it. Part of the year I use it for a space heater drawing 20amps and on the 120v outlet I want to use a small air compressor that draws 10amps.


 

Expert:  Alex replied 1 year ago.
I'm sorry to say that but you can not tap to 240 volt outlet and use as 120 unless you are eliminating 240v. Is it really hard to run new line from panel?
Customer: replied 1 year ago.


It is going to be super difficult to get a new line from the panel so that is why I am trying to make this work. Reading this article led me to believe this was possible: http://www.emgw.org/papers/ShopWiringProof.pdf


 


 

Expert:  Alex replied 1 year ago.
Let me opt out and see what the other experts think.

There are many things possible but not permissible .
Customer: replied 1 year ago.


Ok, do I need to just wait for others to respond? First time to use this forum for anwers.

Expert:  Steve G. replied 1 year ago.

Hello there and welcome to Just Answer. My name is XXXXX XXXXX I will be assisting you today. I am an engineer with over 30 years of electrical and electronic training, repair and installation experience. I will try and answer your question accurately and precisely so that we can get you on your way.

What is the measured voltage across the 240V receptacle? Measure the two hots and also each hot to ground.

Please let me know so that we can continue.

Regards

Steve

Customer: replied 1 year ago.

I am not at home to test it again, but when I tested last night it was 240v from one hot to ground and the other was essentially dead (hot to ground). I have a diagram, let me try to attach.

Expert:  Steve G. replied 1 year ago.

No, I understand.

You can't possibly get 240V from hot to ground so we probably need to have you at the receptacle with your meter so that I can walk you through this.

Steve

Customer: replied 1 year ago.


Ok, in that case I can contact you back in a few hours when in front of the wiring. Also, not sure how to get you the diagram. Each time I try to attach it I get the error below. Let me know if there is another way to send this to you.


Access Denied

You don't have permission to access "http://www.justanswer.com/electrical/7syr5-hello-i-240v-outlet-want-add-120v-outlet-nearby.html" on this server.


Reference #18.56881ab8.1370620938.13e074cf

Expert:  Steve G. replied 1 year ago.

You can email the file to experts@pearl.com marked for my attention (Steve555).

But I don't really think I need it. You have two issues here. 1. Is the arrangement within code and 2. Why the odd voltage readings.

Let's get the voltages sorted first and then we can discuss code stuff.

Steve

Customer: replied 1 year ago.


Thank you. I sent the diagram via email just in case you need it. I will contact you again with the voltage readings when I arrive home later today.

Expert:  Steve G. replied 1 year ago.

Ok, I'll be here. If not, I will be emailed.

Reply only when ready - to keep my waiting list clear..

Thanks

Steve

Customer: replied 1 year ago.

Ok, I had a chance to test the voltage. each hot to ground was ~120v and hot to hot was ~240. All that seems correct.

Expert:  Steve G. replied 1 year ago.

Ok. As a rule, what you are doing is not good practice but, (and I'm sure I will be informed if I am wrong here) there is nothing in the code preventing running some 120V receptacles from a 240v circuit providing:

The breaker is sized in accordance with the receptacles ie. a 2 pole 15A or 20A breaker AND you have a dedicated neutral which you indicated that you do.

If your existing circuit has a 30A breaker - that is not ok. You would have to size that breaker down.

I did get the diagram. All looks good. The usually warnings apply about messing with electricity so please be careful.

Good luck and I'll be here if you need help.

Steve

Customer: replied 1 year ago.
Thank you for verifying the design looks ok. However, the 120v outlet does not work (getting 146v reading on my tester). As mentioned, both hot wires at the 240v outlet read 120v hot to ground. However, what is strange is hot to neutral reads 157v. When I check the hot to neutral in the breaker box (for the same cable) it reads 120v. Shouldn't the hot to neutral in the outlet box read 120v also? How is it possible to gain voltage as the line travels from the breaker box until the outlet area about 30 feet away!?
Expert:  Steve G. replied 1 year ago.

What are the two hot to neutral measurements at the 240V outlet?

Steve

Customer: replied 1 year ago.
in the 240v outlet the black (hot) to neutral is 157v and red (hot) to neutral is ~78v.
Expert:  Steve G. replied 1 year ago.

Yup. So that's not right.

You are going to have to investigate that 240V circuit. Is the receptacle the only outlet on that circuit? Is the neutral dedicated to that circuit or does it tie in with something else?

Please let me know so that we can continue.

Regards

Steve

Customer: replied 1 year ago.
Found it! I noticed the cable leaving the breaker box was romex type cable and then when it arrived to the 240v receptacle it was clad cable. There must be a junction box between. Indeed I found one in the attic and the neutral was capped there. I will connect it and I am sure I will be in business.

One last question on this project. You said not to use a 30A breaker with my 120v outlet. However if I don't plug in anything drawing more than 20A will it be an issue? All cable is 10 gauge and I am thinking the combined load of 10A for the air compressor on the 120v outlet plus the 20A the space heater draws (split to 10A for each hot feeding the 240v receptacle) means the one hot (black) I use for the heater and 120v outlet would have a combined draw of ~20A when in use and the other hot (red) would have a 10A draw when in use because it only feeds the space heater. Since the other side will be right near 20A I am thinking it will trip a 20A breaker often. What do you think?
Expert:  Steve G. replied 1 year ago.

Unless you have a 30A receptacle, it is a violation of the code (and potentially dangerous) to use a 120V receptacle with anything other than a 15A or 20A breaker. The wire size is important but the issue here is the overcurrent protection. Duplex 120V receptacles are rated for 15A or 20A circuits (look on the outlet for the rating).

Given that a breaker should not be loaded to more than 80% of it's nominal rating, your load is excessive for a 20A breaker.

What you COULD do is get yourself a NEMA 5-30 receptacle (30A 120V) but it has a different pin configuration. It may work for you.

The only way around it is to put in a small 4 or 6 pole sub panel and wire a couple of 120V circuits from that. Sorry :(

Steve

Steve G., Electrical Engineer
Category: Electrical
Satisfied Customers: 16908
Experience: 27 years in Electrical Engineering, designing electrical plans and specifications.
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