3 phase motor starter advice

Crohnos01

Member
Location
BG, Washington
I am looking for some advice/references on a question that I thought I knew the answer to, but now I am second guessing myself.

I have a project with a 15hp 230/460v 3ph motor being installed on a subpanel. The MDP is about 200 feet away, and the motor is a 4 pole, 11.2 kW, has a 1.15 SF, NEMA code G and LRA of 256.53 amps at 208 volts (which is what it will be run at... the manufacturer ok'd the lower voltage for the motor already).

My question has to do with starter selection and if a soft start is required. The is no documentation for the MDP loads, however a data logger showed a max peak of 135 amps over a week long period and the MDP is fed by a 15 kVA xfmr about 15 feet from the MDP which is a 208/120 200 amp panel.

I was going to just run a DOL starter, but now I am wondering if I will cause any problems upstream of the motor. The MDP is feeding a mystery building that the client won't let me into to verify loads. It appears to be full of electronics equipment (based on an array of antenna I observed on the roof). It's a government facility; maybe they have the Obamacare website housed there... I dunno.....

Anyway; normally I would not expect the start current to present a problem upstream of the motor on a DOL, but now I am wondering about this mystery building and if I need to error on the side of safety due to unknown electronics present?

Any thoughts or advice?

Thanks,
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
11kW motor fed by a 15kVA transformer, or did I misinterpret what you said? If that's what you have, I would not even bother trying to start that Across-the-Line, you will dim the lights... Soft starter may not even be enough unless it is a really lightly loaded start like a centrifugal pump or fan.
 

Crohnos01

Member
Location
BG, Washington
11kW motor fed by a 15kVA transformer, or did I misinterpret what you said? If that's what you have, I would not even bother trying to start that Across-the-Line, you will dim the lights... Soft starter may not even be enough unless it is a really lightly loaded start like a centrifugal pump or fan.

Actually you're right... I just had my fingers mumble... it's a 75 kVA transformer, not a 15.... sorry for the confusion.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Actually you're right... I just had my fingers mumble... it's a 75 kVA transformer, not a 15.... sorry for the confusion.
Meh, what's 60kVA among friends? ;)

You could easily get away with ATL starting, but not knowing the sensitivity of the black-ops building, I would still opt for a soft starter. Easier to just do it now than to go back in and rip out your work to start over because some secret listening post couldn't focus in on a foreign dignitary's conversation with his mistress...
 

Crohnos01

Member
Location
BG, Washington
Meh, what's 60kVA among friends? ;)

You could easily get away with ATL starting, but not knowing the sensitivity of the black-ops building, I would still opt for a soft starter. Easier to just do it now than to go back in and rip out your work to start over because some secret listening post couldn't focus in on a foreign dignitary's conversation with his mistress...

LOL... yeah, that's kind of where I was at mentally too..... It seems like overkill, but as you point out it's easier now than later when those black helicopters are hovering over my house with guys repelling down to make a surgical strike on me, the terrorist engineer, who caused their porn channel to brown out.....
 

Besoeker

Senior Member
Location
UK
LOL... yeah, that's kind of where I was at mentally too..... It seems like overkill, but as you point out it's easier now than later when those black helicopters are hovering over my house with guys repelling down to make a surgical strike on me, the terrorist engineer, who caused their porn channel to brown out.....

Maybe you could repel the repellers.....
:p
 

Crohnos01

Member
Location
BG, Washington
Maybe you could repel the repellers.....
:p
You have noticed the reason I went into engineering instead being an english major.... Without freaking spell check, I wouldn't be able to communicate except for sign language.... and that's not too hard.... it only requires one finger apparently.... or so I observe when driving down the road.....;)
 

GoldDigger

Moderator
Staff member
You have noticed the reason I went into engineering instead being an english major.... Without freaking spell check, I wouldn't be able to communicate except for sign language.... and that's not too hard.... it only requires one finger apparently.... or so I observe when driving down the road.....;)
Actually the two finger ("alternating double bird") would be more common if the other hand were not busy holding the cell phone. :)
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Actually the two finger ("alternating double bird") would be more common if the other hand were not busy holding the cell phone. :)
The other day I was driving on the freeway and saw some teenage girl gabbing on her cell phone while driving. I gave her a one finger sign, but she ignored me. That made me so mad I had to throw my beer at her...



I know, I know, this is a modification of what's already an old joke now. I just couldn't resist, it's one of my favorites.
 

Besoeker

Senior Member
Location
UK
You have noticed the reason I went into engineering instead being an english major.... Without freaking spell check, I wouldn't be able to communicate except for sign language.... and that's not too hard.... it only requires one finger apparently.... or so I observe when driving down the road.....;)
Forgive me - it was an opportune attempt at humour.
When I started secondary school, aged eleven, one of the homework exercises for English was to write an essay each week. It was marked for content, grammar, and spelling. More than a few incorrect spellings earned you "the belt". This was a smack on the outstretched hand with a heavy leather strap wielded in a vicious arc by the English teacher. I got it - once. My spelling immediately improved.

Sorry mods. I know it's off topic. But be kind.
 

jumper

Senior Member
Forgive me - it was an opportune attempt at humour.
When I started secondary school, aged eleven, one of the homework exercises for English was to write an essay each week. It was marked for content, grammar, and spelling. More than a few incorrect spellings earned you "the belt". This was a smack on the outstretched hand with a heavy leather strap wielded in a vicious arc by the English teacher. I got it - once. My spelling immediately improved.

Sorry mods. I know it's off topic. But be kind.
I thought it was funny.
 
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