How Much In-Rush Current on 7.5 HP RPC Startup?

I've been threatening to build a 7.5 HP RPC for some time now. Was talking about this w/ a friend who remarked that it will be a huge in rush dimming the lights all around me. I really don't know myself?

My shop is in a 22 year old townhouse development. My shop is in the garage in the lower level. The 240 Volt, 200 amp single phase service panel is right there in the garage. I would put a dedicated breaker for the RPC into the breaker box.

Just trying to get an idea if this 7.5 HP RPC is maybe too much w/o causing trouble for the neighborhood (and ire of the power company) w/ lights dimming etc. This is a home shop, use is infrequent.

The biggest 3 Ph machine will be a 1945 MG monarch 10EE, and a 3 HP unisaw that I would like to run from the RPC.

Wondering if perhaps I should build a 5 HP RPC instead to reduce inrush demand on startup. Will using a pony motor to bring the idler to speed before powering the 7.5 HP idler reduce inrush current?

Pic of 7.5 HP idler nameplate is HERE

I have a 7.5hp RPC and yes the lights dim slightly on startup. But they dont go out or anywhere close. I have not measured the inrush but expect it would be considerable. I also use it infrequently so dont mind the dimming lights. That way my wife knows Im busy in the shop. The pony motor would definatly reduce the inrush but dont have a feel for how much, maybe someone else has some experience with that.

wm

my 7.5 is a 1740 rpm and says 21.6 amps fla. my digital fluke cant catch the start up inrush but my old and trusty amprobe analog shows 50amps at start up. i use the push button method and dont even think about the timing anymore. my lights dim very little and for maybe 1/2 to 3/4 of a second. it is no worse than what the normal poco spikes and droops are. if your worried about the startup draw pony start it

If you use a pony motor to spin the idler up, the extra inrush current is just about
zero.

Jim

The wiring required to start the motor on 110 volts (low voltage start= low inrush) Is barely different than full voltage start and run circuit. A neutral is required certainly.

I have a small 220/380V 3ph motor spinning merrily on the work bench started with capacitors all on 110V

I wish I knew a way to "copy an image" for posting. No scanners here.

Regards

Cal

I ran my 10hp RPC (capacitor start, balanced capacitor run) for a year with a 40A breaker on 6ga branch wiring. Never had any trips. My largest load was a soft starting 7.5hp lathe, so that might have something to do with it.

No issues with lights flickering, but then they're all T8's in the shop. The wife never mentioned any issues in the house in conjunction with my activities in the shop. But my tig welder dwarfs that current demand by double and it never causes any issues either.

If you build a cap / potential relay start and use two 270-324 mfd electrolytic start caps then you should have no problems. I have a couple of these in use in home shops with 200 amp panels. The lights do not even flicker. They are both on 60 amp circuits though. You need a minimum of a 40 amp circuit for a 7-1/2 hp but I use a 60 amp design just in case the owner ever needs to upgrade to a 10 hp idler.