New Member - Electrical question for Exhaust Fans

[wcg89]

Hey guys, I'm new here this seems like it's going to be a very useful site for me.

I am installing two 3-phase 48" cabinet exhaust fans, each fan only pulls 2.9 amps @ 460V.

The main breaker box is outside and there is a junction box on the inside of the building that I will be hooking into for power.

I'll be honest with you guys, I am NOT an electrical engineer! Electricity confuses me for the most part, but I have this project to get done and I am trying to do my research and willing to learn! I just want to do it right the first time.

With that being said y'all take it easy on me if I am asking dumb questions.

Questions:

1. There is way more than enough room on the existing panel to run these two fans. From my research I have done so far, I am planning on using a 3-pole 20 amp breaker and #12 AWG wire. Will this be OK?

2. I will be putting a safety switch in and I have looked at fusible vs. non-fusible and decided to go with fusible just for an added safety precaution. From common sense I am also assuming that the safety switch will be wired in between the junction box and the fans. Is this correct?

3. How do I determine what size conduit I should use?

4. I am going to put in two on/off motor switches so the workers can leave the safety switch in the ON position unless maintenance needs to be performed on the fans, I figured this allows me to put the two motor on/off switches in a more convenient place for the workers to get to and they can just flip them on without having to walk over to the safety switch.

That being said, my question is; if I am using #12 wire to run power to the fans, do I have to use #12 wire to run power to my two motor switches? If not, which size wire would be best?​

Link to the fan I am installing: <a href="<a href="

http://www.grainger.com/product/DAY.../image/Grainger/1AHB6_AS01?$smthumb$">Exhaust

Fan</a>

Link to safety switch:
<a href="

http://www.grainger.com/product/SQU...2JXU1_AS01%3F%24smthumb%24&s_pp=false">Safety

Switch</a>

Link to motor switches:
<a href="

http://www.grainger.com/product/SQU...ls=1&nlsit=0.8&ssf=2&searchQuery=1h401">Motor

Switch</a>

 

[berkshire]

Why not take the worry out of this job, and just hire an electrician to do it?
B.E.

You are judged not by what you know, but by what you can do.

 

[wcg89]

Why not take the worry out of this job, and just hire an electrician to do it?
B.E.

I will be hiring an HVAC company to do everything and he will probably hire the electrician or do it themselves. I am designing and managing the project, I can design everything else for the project and have been researching my electicity the past couple of days, but I am wanting people that know what they are talking about to answer my simple questions. I'm new to this whole designing/managing process.

 

[berkshire]

wgc89,
So far it appears you are on the right track, I have some electrical experience , but I am not an electrician. I have HVAC experience.
Based on what you have written here, you need to have a conversation with an electrician and the HVAC guy , about how you are going to run your cables, and to confirm your wire and breaker selections. Also decide on what voltage you are going to run this system at.
B.E.

You are judged not by what you know, but by what you can do.

 

[EnergyProfessional]

Not an electrical engineer either, but I took an electrical engineering course specially for non-electrical engineers and one of my employees is a master electrician. so take what I say with a grain of salt:
- code allows #12 for 20A breaker. but industry standard is to have #10 wire for 20A (if very long runs even thicker wire to avoid voltage drop). This may not be a problem for you since you only have 2.9 A (is this nameplate, or did you measure? you need to use nameplate.... that number will vary with actual airflow)
- you may use 15A breakers, then #12 wire is appropriate. (Again, this is above code, but industry practice)
- the fuses should be sized for the motor to protect it from overload. Motor manufacturer may tell you 5A or whatever. Your 15 or 20A breaker won't trip before 30 or 40 A whne there is a short overload (breakers take into account current and time, they kind of integrate). the fuse reacts very fast and size is matched to the motor.
- the code-required disconnect must be near the device and clearly labelled and visible. Ideally it has a lockout with padlock so no one turns the thing on. Yes the disconnect is between the brekaer and the motor. Junction or pull-boxes in between don't really matter. I assume each motor has its own branch and you don't put lighting on the same branch or so.
- i recommend buying the NEC commented version. I believe this handbook is what I mean. this contains the electrical code, but also has comments, graphics, and examples explaining. I think for non electricians and non-electrical engineers, this is very valuable. thsi will tell you about conduit sizing. not sure how that is done in you area, but normally this is responsibility of the electrical contractor, at least where I live. but for such simple example you can do it. If in doubt, upsize the conduit. with your #12 wire it should not be large anyway. Keep in mind neutral, ground etc. are treated differently when it comes to conduit sizing, it all is related to cooling the insulation and being able to pull the wires without damaging. Obviously if some of the conduit part way is used for other branches (and split at a J-box) this becomes a bit more difficult.

 

[EnergyProfessional]

To add, whatever the code requires is not sufficient for a good installation. Code mainly is concerned with the insulation not degrading and burning down the building. Until the 1930's human life protection was not even considered because the building insurance industry (who drove the code) didn't insure lives. Now, not burning the (insured) building and not killing (insured due to liability nowadays) are the main concerns. code allows bad practices (shared neutrals, aluminum conductors) that don't kill people and burn down buildings. So be above code where it make sense to be "better".

 

[wcg89]

Thanks for your replies Berkshire and EnergyProfessional.

EnergyProfessional,

I'll look into he different sizes of breakers and wires.

I put the links to everything I am looking at ordering at the bottom of my post. The fan specs are where I got the 2.9 @ 460V from. Also, if I end up using #12 to run power to the fans, do I need to use that same size wire for my motor switches? Or can I go smaller?

And I'll probably be ordering that book soon, thanks.

Also, I will search for it in a little bit but do you know how close the safety swith needs to be? The fans will be 36 feet apart center to center. The junction box is close to one fan, within 3 feet.

 

[RossABQ]

It sounds like you are going to run both fans on one circuit? I wouldn't do that, if for no other reason than maintenance.

 

[ScottyUK]

wcg89,

I'm not going to answer your question directly because I don't have sufficient knowledge of the NEC: I'm in England, and we have a different set of rules to work to.

If the NEC has half as many obscure requirements as its British equivalent - and I'm pretty sure that it does - then you really need to get an electrical design engineer to look at this. I've been doing electrical work for more than half my life and I certainly don't know everything in our Wiring Regulations. You're almost guaranteed to miss something if you try to do this on your own, which is sort of OK (but it's not really) provided nothing goes wrong. If something does go wrong and you're at fault either through intent, or through ignorance of the requirement, or through error then you're likely to be in trouble. It's not worth whatever you're saving by doing it yourself.