Equipment current ratings

Hey guys. We have a Hytronic brand press here at work. It's a small hydraulic press, and its fed with 240VAC 3phase. It's mostly just a simple hydraulic press, but the motor nameplate is unreadable, and I have no manuals. On the side of the press, there is a nameplate which has the following ratings. Rated Current 10 Amp Rated Current Fuse for Mains 25A. What I am wondering, is what do these ratings mean. Are they the rating with which to size the conductor and OC protection, or are they to be used for SC protection. Also, which # should be used. The fact that both ratings are there confuse me. Right now it has nuisance trips when the motor starts, and I would like to know exactly how much larger I can go, but really don't have anything concrete with which to base my theory on. Has anyone seen these ratings before on industrial equipment that can elaborate some?

Russ

The nusiance trips- do you have a time adjustable breaker? If you do, turn it up to allow the motor to start up.
Can you put a VFD or a soft start on the motor? (Easier mechanically & eletrically)

No and no. The only protection now on the secondary side of the feeder transformer is a fused disconnect with 20 amp fuses. I don't know how the 20 amp fuse was decided upon, but before I go upsizing, I want to have an idea what is NEC legal. I am a little confused about the 10 amp rating, if I should size the mains at 25 amps, why even show me the 10 mp rating?

What type of fuse do you have? If the fuse is a fast blow, even if it's oversized, it won't allow the motor to come up to speed.

The 25 Amp feed is probably what you need to have your feeder circuit breaker at most, and the 10 amp is for the transformer protection. Do you have a schematic you can post of the machine?

Ive got basically nothing, except for said nameplate on the side of the equipment. I can't even tell you what the horsepower rating of the motor is, the nameplate on the motor is gone. Arrrgh.

Was it running alright before? If it was, then the real question is not how high can I go, but what has changed that is causing a greater current draw. Too many times I've seen in plants the adjustable overloads maxed out because of "nuisance" tripping. Eventually, we replace the burned up motor and the resultant cause of the change (gearbox, bad bearings, etc.). Has the voltage changed any (lower voltage causes higher motor currents)?

more info

is the machine quite old and has a valve controller in it and is bascilly a small dye cutter

Yes, it is a small die cutter. They use it to cut samples of material I guess. Yes, it was running before. But it has been moved, and has not run without the nuisance trips since moving. I highly doubt anything has changed, other than the protection coming into the press. Under normal op conditions it only draws about 6 to 7 amps, and about 12 when actually cutting. I don't think that this is excessive for this machine in any way, so I think it's just popping fuses when they first start the machine. I was basically wondering if machines like this usually come with ratings to use for sizing OC and SC protection, and if so, what the ratings this one gives mean.

My guess is the main fusing is 25 amps, and the 10 amp rating is to show a typical current draw under normal operation.
If the motor is 5 HP, you should be able to fuse at 25 or 30 amps safely.
Check the charts starting at page 145 on this link from Bussman:

http://www.bussmann.com/apen/pubs/spd05/index.asp

The other issue is the feeder transformer. Is this a dedicated transformer rated for 20 amps? If so, you can't upsize the fuses without compromising the transformer protection.

The proper type of fuse is important in this application. There's a wealth of info that should help in the link above.

check supply valve

if this is the same as the machine i have worked on the soleniod valve is a proportional valve and if fully on on then the pump maybe starting under full load
when then cutter comes down under the bottom plate is mesh plate which makes contact with the blade and via the old electronic valve turns of the hydralic valve
if the plate and blade dont make it keeps supply hydralic pressure for to long

Russ,

Both of those numbers should be used. For motor circuits with high starting currents, you need to know the normal "running" current, probably 10 Amps in this case, but you also need to know the allowable and required size of the breaker or fuse necessary to get the motor from 0 to normal running speed. The US National Electrical Code, Table 430-150, shows that a 3 horsepower, 230 volt, 3-phase motor has a normal full-load current of 9.6 Amps. This is probably your "10 Amp" rating.

NEC Table 430-152 gives the maximum allowable setting of fuses and breakers for motor branch circuits. For AC 3-phase motors, with fuses it is 175% of FLA, and with circuit breakers it is 250% of the motor FLA. However there is an exception to the rule in Article 430-52(c) that allows time-delay duel element fuses as high as 225% of FLA. Assuming your motor has a 10 Amp FLA, then the code allows you to use time-delay fuses as large as 22.5 Amps (probbaly your "25 Amp rating). Your wiring and starter must also be rated for the same level, #12 wire for 20 Amp fuses, #10 for 25 or 30 Amp fuses

The max fuse size is based on using the motor at rated voltage. If it is a 480/240 volt duel winding motor, and you are running it on 208 volts, then it will pull about 10% more current, and the fuse will have to be raised accordingly. I noticed you said it was "fed with 240VAC 3phase". Do you realize how rare it is to have an actual 240 volt 3-phase AC voltage supply? I see a lot of 208 volt 3-phase transformers that are running on the 4th tap, so that you get maybe 218 volts if you are lucky.

If you are using 20 or 25 Amp Class J, K or some other duel-element type on a 3 HP motor, and the voltage actually measures 240 with a meter, and the fuse still blows, then there is a problem with the motor or hydraulic pump.

Because the motor has been moved from a previous location, I would check the voltage first.

Lancie,

Based on what you have said, you are sizing the branch cicuit short circuit protection. This is what I was wondering. As it is, the press is now fused with 25 amp fuses, which is probably correct. It is supplied with 240 V 3 phase. This was verified when the fuses first blew. It is fed directly from is own isolation transformer, which was installed when the press was moved. I am not positive, but I believe it is a corner grounded delta secondary. That's really irrelevant to my question though, as I'm sure the transformer is protected on the primary side properly. You did answer my question thoroughly. I am confident that the 10 amp rating is a normal load rating, and the 25 amp is the rating to use for BCSC protection. As far as I know, we haven't had a trip since installing the 25 amp fuses. Originally, the guy who wired the incoming power placed 10 amp fuses per the other rating. Thanks for the explanation. This is what I thought, but wanted some reassurance.

Russ