240V Power Srip?

[metman]

Our local electric supplir says ther is none such. Is this true and if so why?

By Power Strip, I mean like the device that is made for 115V service that plugs into a receptacle and has two or more female plugs usually encased in a metal or plastic enclosure. I suppose a surge protector would be a special case of a power strip.

 

[Bung]

You can buy them at any supermarket here in Australia. I presume you mean the gizmos that allow you to plug more than one appliance into a wall socket by providing a strip of 4 sockets on the end of a short lead with a normal plug at the other end?

ie P--------[SSSS]
Pis the plug, S are the sockets on the other end of the lead ----.


Bung
Life is non-linear...

 

[Myndex]

The Aussie "smiley face" plugs won't fit American sockets, however.

The lack of 220 powerstrips here is due to the fact that virtually all our appliances work on 110-120. the few devices that use 220 generally are of such current needs that they get their own dedicated circuit, so a powerstrip would be superfluous.


Andy

 

[metman]

Thank you Myndex. I suspected as much. This is in the workplace for a special test. We have three motors to be energized and only two outlets one being at least 100ft from the test. So I guess We'll make our own powerstrip. The outlets are for welder plug-in so there are ample amps available.

 

[buzzp]

Sounds like you have bigger issues. Breakers and conductors need to be sized for motor loads. Your outlets are probably not designed for motor loads. In addition, each motor should have a contactor to carry the in rush current of the motor at start-up. A standard light switch will not work. Need to have OL protection as well if your fuses are not rated as motor overloads. Best be careful and best talk to an electrician, at least. What HP are these motors?

 

[metman]

buzzp,
One motor is 2 hp and the other is 5hp but they will not be loaded to FLA and will not be necessary to start them simultaneously. I believe these are used motors that were available and don't really need this much capacity. The circuit is good for 50 amp.

I appreciate your concern, especially the comment about the switch (maybe we could use a Frankenstein switch), and will take it under advisement even though it is not my responsiblity, I will make sure that sometning dangerous is not attempted.

The third motor I have not seen but it will not be under load (possibly idling) when the two above motors are energized and this is a separate outlet and hopefully an additional circuit. I will check this.

Thank you

 

[buzzp]

Generally, contactors or starters (contactor with built in overload protection) are used for energizing a motor. You might check into this. They would be fairly cheap for these motor sizes. Just keep in mind that when you energize a motor it will pull LRA (locked rotor amps) momentarily. The LRA is generally 6-10 times the full load amp rating found on the motor. My NEMA book is showing a MAXIMUM locked rotor current for a 230V 2HP motor is 50A and for a 5HP 230V it is 92A. Depending on your breaker (the one protecting the 50A socket) it may trip when you start the 5HP motor, depends on the trip curve of the breaker.

 

[metman]

buzzp ,
Thanks. I have copied and pasted your response in a word doc for later email to the mfg engr in charge of the project.

I looked at your profile but could not tell if you are an EE or...?

I was told by an ME that I worked for that LRA was approx 3X FLA and I believed him because he was sharp. The FLA rating of the 2 hp motor was 15A as I recall which works out to 3.33X at the NEMA listing you quoted of 50A. Where does the 6-10X factor come from?

 

[ScottyUK]

Metman,

buzzp is right on the mark with LRC being 6-10x FLC. The exact value is dependent on the design of the motor's magnetic circuit. There is a fair bit of variation depending on what the goal of the designer was: high pull-out torque, high efficiency, low starting current, etc.



----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[Bung]

If you are using a 100ft lead from outlet to motor, then the LRC could well be less than 6-10x due to voltage drop on the cable...

Bung
Life is non-linear...

 

[jraef]

Motors take special plugs because of the possibility of them coming unplugged under load, which will draw an arc and the aforementioned LRA that the motor will draw. I think that you will find (if you check) that the average cord type plug, regardless of amp rating, is only rated for 1/4HP or maybe 1/2HP. You will need a motor rated plug and receptacle system for these, as well as a disconnect switch. There are several manufacturers who offer integrated motor pug / disconnects which do not allow you to unlock the plug and pull it out unless the disconnect is off. Crouse-Hinds is one, Appleton and Hubbel are others. Another alternative is Meltric, who make a plug and receptacle combination that are specifically rated as disconnect devices. That is the one now used in most industrial / commercial portable motor connections.

"Venditori de oleum-vipera non vigere excordis populi"

 

[buzzp]

I am an EE. The LRA's comes from NEMA guidelines. 6-10's is the numbers used by most EE's. You might see some saying only 6-8 times instead of 6-10 times. This is a rule of thumb. The numbers I gave you is the data the motor should be operating within.

I show full load amps of a 2HP, 230V squirrel cage motor to be 6.8A with locked rotor current (max) of 50A.
The 5HP 230V shows full load amps of 15.2A with locked rotor current of 92A. So these are roughly 6X the full load current. Looks like you confused the 2HP and 5HP.

Now I am sure your ME boss is sharp but if your motors are designed aroung NEMA and are squirrel cage induction motors then the numbers I give you are correct but are the maximum numbers.