5hp Motor Control Question

Reply

  #1  
Old 06-26-08, 09:03 AM
Member
Thread Starter
Join Date: Jun 2008
Posts: 2
Received 0 Votes on 0 Posts
5hp Motor Control Question

I am in the process of installing a large irrigation pump, which is to be the sole load (except for a convenience receptacle) on a standard 100amp service. I am confused about the need for a motor starter, overload protection, and disconnect.

The irrigation system will run infrequently (< 4 times a day) and will largely run unattended.

The motor in question is a 5hp Myers Centrifugal pump rated at
1-phase, 230v, Code Letter J, Service Factor Amps 29.9, and Locked Rotor Amps 174. The motor is not thermally protected but is rated for continuous duty.

The one-way distance from the motor to the electric service is 240 feet. Based on Section 430 and 310 and also a desire to limit voltage drop to 5%, I have calculated that I need #6THHN wires in sch40 conduit to carry the load.

Q1: For a motor load, it seems that I would use a 40 amp standard 2-pole circuit breaker for this line (< 250% of Full Load Amps), but I don't understand how the locked rotor current might affect the breaker, nor am I sure that the 10000 amp interrupting limit on standard circuit breakers is enough. Are there other things I need to consider when selecting the breaker?

Q2: I will need a disconnecting means and overload protection near to the motor, I believe, but I have no idea what type of product to look for or how to size the overload protection (though <115% of FLA seems like a safe bet). Can anyone point me to what product/size I should look for?

Q3: Since the motor is the sole load (except for a convenience receptacle) on this service, I tend to doubt that I need a separate motor starter, but I am fuzzy about why/when a starter is required. Myers recommends a "properly sized magnetic motor starter", but does not appear to require it. If I do need a starter, can I get one that is integral with the disconnect and overload protection?

Q4: The motor will be controlled by a ESP-M4 controller from Rainbird. I do not believe that this device is capable of switching such a large current as this motor will draw. Will I need to put in an additional relay to switch the current, or will the overload/disconnect/starter handle this?

Sorry for the long-windedness, but I thought it better to put in all the detail up-front.
 
Sponsored Links
  #2  
Old 06-26-08, 09:28 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by pditmars View Post
I have calculated that I need #6THHN wires in sch40 conduit to carry the load.
Yes, #6 copper would do fine. You also may want to consider #4 or #2 aluminum when you see the price of #6 copper.

For a motor load, it seems that I would use a 40 amp standard 2-pole circuit breaker for this line (< 250% of Full Load Amps), but I don't understand how the locked rotor current might affect the breaker
The 40A is standard for a 5HP motor. Modern breakers carry an HACR rating which allows the momentary start-up surge without tripping the breaker. The behavior is similar to a time-delay fuse.

I will need a disconnecting means and overload protection near to the motor, I believe, but I have no idea what type of product to look for or how to size the overload protection (though <115% of FLA seems like a safe bet). Can anyone point me to what product/size I should look for?
A two-pole fused disconnect will work just fine; they're most commonly sold for air conditioners. It should be about $10. Look out because these come in both fused and unfused, so check the package closely. Be sure to buy time-delay fuses for it; standard fuses will burn up.

A disconnect is required at the motor, but may not be required to be fused if you get a starter with overload protection (see below).

...doubt that I need a separate motor starter, but I am fuzzy about why/when a starter is required....

The motor will be controlled by a ESP-M4 controller from Rainbird. I do not believe that this device is capable of switching such a large current as this motor will draw.
Question 4 answers question 3 about the need for a starter. A magnetic starter is basically a relay switch that allows your irrigation controller to switch the large motor load. The starter often will have a thermal overload relay built-in too.

Does your ESP-M4 controller operate on 120V or 240V? This will determine the coil voltage for your starter. If you take the motor specs to a motor shop or an electrical supply house they should be able to order you an adequate starter; this is not something you will find at the big box.
 
  #3  
Old 06-26-08, 12:40 PM
Member
Join Date: Oct 2005
Location: USA
Posts: 1,452
Received 15 Votes on 15 Posts
is the 120v recept local?

If so, then the disconnect box may turn into a subpanel, with the double pole breaker and then a GFCI breaker for the 120v receptacle.
In any case, you will need to find or design a motor starter, using a 24VAC contactor coil. Irrigation controllers will generally supply a "master" valve voltage. It is this voltage that will pull-in the motor contactor. You need to decide if you want "local" control. THat is, what happens if the rainbird breaks; do you want bypass control? That complicates the design slightly.
Also, if exposed to the elements, the electrical box(s) should be NEMA 4 or 4x rated.
Find motor overload heaters, that can be adjusted to the 5 HP load current.
Last comment; if you do have 3 phase nearby, use it, rather than single phase. It makes for a more reliable motor (no caps, no start winding, no start switch). It will require one more conductor. If no 3 phase, then don't worry about it.
 
  #4  
Old 06-27-08, 11:51 PM
Member
Join Date: Jul 2007
Location: California
Posts: 22
Received 0 Votes on 0 Posts
Originally Posted by telecom guy View Post
Also, if exposed to the elements, the electrical box(s) should be NEMA 4 or 4x rated.

NEMA 3R will do the job at a whole lot lower cost NEMA 4,4X cans are quite costly,nice but overkill.
 
  #5  
Old 06-28-08, 07:23 PM
Member
Join Date: Oct 2007
Location: Delray Beach, FL
Posts: 406
Received 0 Votes on 0 Posts
Agreed.
Unless you are in a corrosive atmosphere, you can use the 3R.
4X is stainless steel and will cost several hundred dollars not to mention probably 2 or 3 weeks to get it from a supplier.
 
  #6  
Old 06-29-08, 09:00 AM
Member
Join Date: Jun 2008
Location: VA.
Posts: 813
Received 1 Vote on 1 Post
Here is an example of a combo starter. You will need to use a starter if you want your controller to control the motor and you'll need a 24vac coil for your starter. I would recommend a pressure tank and pressure switch also. If your valve(s) failed the pump turns on and it'll blow your pipes apart.

http://www.us.schneider-electric.com/us/products/nema_contactors_starters.nsf/unid/1202DED0E3A3BBC585256B05004B544F/$file/combostrtrs.htm
 
  #7  
Old 09-24-08, 12:27 PM
Member
Thread Starter
Join Date: Jun 2008
Posts: 2
Received 0 Votes on 0 Posts
Results of Project

Hello all,

Thank you all for your input. All of it was helpful and contributed to a successful project. I will describe below how I installed the system, which is working very well now, and while it may be a little unorthodox, I believe that it is safe.

One thing that I did learn in the process, is that the best electrical plans often have to be adapted to what the local suppliers have in stock. I was forced to make several compromises when the parts that I located in a catalog had to be special ordered at a very special price.

Another thing that I learned is never to trust the published specs on a motor. When I ordered it, the motor listed 29.9 as FLA. When I got it, the nameplate said 26 amps!

I ran #6 copper in underground conduit from a 60amp breaker in the Service Entrance to a 100amp subpanel at the motor site. I did this because I needed a convenience receptacle at the site (on a separate 20amp breaker), and adding a 40amp circuit breaker at the subpanel (in sight of the motor) was a convenient way of providing a disconnect.

On the same pedestal, I mounted a NEMA 3R box which enclosed a Rainbird Controller, a motor starter relay/overload combo, a motor dry well protector (see below) and a relay to connect the Rainbird controller to the motor starter.

I used 3phase motor starter/relay from Telemechanique, since this cost was 1/2 of what a 1phase starter would cost at my local suppliers. I was advised to loop the output of the middle phase of the starter to the input of the 3rd phase (T2 -> L3) to avoid phase shift problems, and I did so. The nice thing about this starter relay, is that it has dial-settable overload protection, so I was able to set it to exactly what I needed based on the motor specs.

I used a product called the PumpSaver Model 235 in order to detect dry well conditions. This product also detects overload conditions (dead head), though the motor starter/overload relay should handle this. Basically, the PumpSaver is a current transformer on one of the motor input lines (L1) which supplies an input to a small microprocessor which monitors the input for irregularities. When something wierd comes up, it shuts down the other input line (L2). I tested it with both dry well and dead-head conditions and it worked properly.

I used an inexpensive relay to allow the output of the rainbird (24v) to switch the output of the PumpSaver (120v), allowing it to control the coil of the starter/overload unit.

The output of all this (240v to the motor and 2 24v control lines to solenoid valves) was fed into a buried (and grounded) meter can which contained a plastic NEMA 4 box for making connections.
 
  #8  
Old 09-24-08, 03:42 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Glad it's all up and running! Thanks for posting back with a status update. I think someday you'll be glad that you added all of that extra protection to the pump.
 
  #9  
Old 09-24-08, 05:36 PM
Member
Join Date: Apr 2007
Location: Near Buffalo, NY
Posts: 4,239
Received 0 Votes on 0 Posts
Pardon me for butting in here ...

Is this irrigation system for a home? I noticed the brand name "Rainbird" mentioned here and was kicking around the idea of installing a basic lawn & garden system to save my wife from dragging hoses all over the yards to water her gardens.

Am I to understand that I have to upgrade my electrical service (currently 100 amps) to run a pump to accommodate 5,000 square feet of gardens?!?!
 
  #10  
Old 09-24-08, 05:44 PM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
Rick .,,

It depending on the pump size and the exsting load you have in the house some case you can get by but you may want do the load demand caluaction to make sure you are safe side if feel too small you can upgrade to 200 amp which it is a common size.

Cost wise that part I just can't really comment due so many diffrent variations it have to be involded and if you going upgrading normally I rather have a electrician to come out and they can do it for ya due 1) the speed of hook up the box 2) they have to know the latest code and get it safe as need to be. 3) the number of connections in the box when it upgrading if not carefull it can get ya.

If you have 3 HP or less I don't really think it will be a issue with 100 amp service unless you have major applainces are electric { no gas } it can change a bit.

Merci,Marc
 
  #11  
Old 09-24-08, 09:46 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Rick, the OP must be irrigating a large area with a 5HP pump or running all of his zones at the same time. This size pump should be able to output somewhere in the neighborhood of 200 gallon/minute at normal pressure.

A residential sprinkler head should output about 1-3 GPM. You would normally have about 10-20 heads on a zone, and a handful of zones in a city lot yard. The controller cycles through the zones so that only one is active at any given time.

Rainbird makes everything from tiny drip irrigation systems to golf course and agriculture irrigation systems.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: