Rated amperage vs actual on equipment

[merchmonster]

What's the best way to figure this out? Our equipment in the shop is over the rated load for the box but we don't have problems with breakers tripping when everything is on. My understanding is that this is because machines draw more heavily when heating up then reach a cruising altitude where they draw less energy.

[Maxie]

I don’t think there is any way to figure this out accurately.
I moved my plant last year and in theory don’t have enough current to run everything but like in your situation everything works.
What I figure is that we have 2 automatics, 4 flashes, compressor, pressure washers etc but rarely does everything work at the same time.       We don’t run all the heads at once and the flashes are not all on at the same time so what we need in theory is not what is used in practice.

[mooseman]

What's the best way to figure this out? Our equipment in the shop is over the rated load for the box but we don't have problems with breakers tripping when everything is on. My understanding is that this is because machines draw more heavily when heating up then reach a cruising altitude where they draw less energy.

My understanding is that this is because machines draw more heavily when heating up then reach a cruising altitude where they draw less energy.
I am not an electrician bit I don,t believe this is actually true. When the machine ( your dryer or flash) is warming up it is drawing all the current it needs at a staedy rate. It is not like the cruise control in you car that will well over rev your engine at high RPM to run back up to the set speed and lower cruise RPM.
The only real time you dryer draws higher current is the very few nano-seconds when you turn it on. It is basically called inrush current.
Because the electrical conduit has no current it has the ability to draw a great deal of current untill the electrical conduit is filled so to speak. You can often see this in a light bulb the blows the very instant you switch it on. The element draws high current for just a few nano seconds because it has no load or current therefor a large capacity (emptyness) to take current. I have seen super slow motion video of a bulb lighting up. the element actually shutters and over glows evev so slightly until it hits normal current load.

The final answer is simply to get an amp meter thro it the the feed line and see the actual ampaeage starting up and running.

FYI
Inrush Current Causes and Cures. Learn about Inrush Current Limiters
https://www.ametherm.com/inrush-current/
Inrush Current Limiters are used to reduce the inrush current that occurs when an electrical device is switched on. High inrush current is the result of the maximum instantaneous input current drawn by an electrical device during the initial power up.

mooseman

Inrush Current Solutions
Inrush Current Limiters are used to reduce the inrush current that occurs when an electrical device is switched on. High inrush current is the result of the maximum instantaneous input current drawn by an electrical device during the initial power up. As technology continues to advance, most systems today run efficiently and maintain a low impedance which in turn contributes to high inrush current.

Additionally, devices that produce alternating current such as electric motors or transformers can draw several times their steady state current at switch on. Although this additional draw of inrush often lasts less than ½ of a normal 60 hertz cycle, that is enough time to cause possible damage to the equipment.

[Northland]

What's the best way to figure this out? Our equipment in the shop is over the rated load for the box but we don't have problems with breakers tripping when everything is on. My understanding is that this is because machines draw more heavily when heating up then reach a cruising altitude where they draw less energy.

If you are pressed for time.... skip to the final paragraph.

The most accurate (albeit expensive) way is to conduct what is known as an "electrical load study".  The study shows how much power is being used and when it is being used.... it would capture peak power demand which is probably your primary concern. To be valid, the study would need to also include power used during peak heating/cooling periods. An engineering firm could perform this task (some electrical contractors would also be equipped to provide this service)

How it works:
Two different types of sensors are connected to the main distribution wiring. This allows you to measure both voltage and current simultaneously. The sensors are connected to a meter that records the data at a predetermined sampling rate (usually one reading every 5-15 minutes). When the data is downloaded to a PC (usually formatted in Excel), the data can be displayed however you wish (often a bar graph works well). The equipment is moderately expensive, so this isn't your typical DIY project.

https://www.amazon.com/Extech-PQ3450-12-3-Phase-Analyzer-Logger/dp/B00APD10JM/ref=sr_1_7?ie=UTF8&qid=1509234134&sr=8-7&keywords=power+logger

If your peak load is less than 80% of your available capacity, it is considered safe to add more load (equipment).





The quick & dirty way, to estimate your load, is to total all nameplate current ratings your "major equipment" and multiply that number by 70%.
Most motor and heating loads will cycle Off/On during use and this creates a "diversity" situation where only 70% of the equipment is using power simultaneously.
Simplfied Example:
Air compressor        30 amps
Conveyor dryer       60 amps
Flash                      30 amps
Flash                      30 amps
Shop AC unit           60 amps
Total                       210 amps
70% diversity          147 amps
This is a crude estimate... but helps explain why you don't have "Main" circuit breaker tripping problems during operation.

[ZooCity]

Get a quality clamp meter and read amperage on each of your dedicated circuits to equipment while it's running.  You do this at the panel so have an electrician do it if you are not comfortable.  You'll find that many of your machines spike initially and then level out to a running amp draw that is far lower than the fla on the plate.  The device Northland linked is a super nice tool for this but quite a bit of coin.  I've done it by simply taking multiple readings with a single clamp.  Not perfectly accurate but definitely good enough.

Our rotary compressor for instance draws a ton of amps when the motor kicks on and then sips amperage once started up.  If it had a soft start we could probably safely use more amps overall in the shop.

Same with your quartz flashes.  You can alleviate some of that load by offsetting their start by a fraction of a second or so if you have that option on them.

Most other equipment isn't going to spike on you although some of it will have serious in rush current.  Our Eco is on a 150a shutoff/breaker for this reason.  It has 2 flashes and the press all wired together.  Now, it never draws that much in operation, even when running with both flashes full tilt boogie but will draw up to 120+a at turn on for a very brief moment.  Items with in rush like this need wiring and breaker to accommodate or you end up using your breaker every morning like a light switch when it trips and then you turn it back on and that's not good form.  Breakers aren't switches and their performance will fall off if you use them as such. 

Essentially, just identify the pieces that draw hard when firing, ensure that you aren't using your breakers like switches due to in rush at start up and then keep the load spread out.  If this is all accommodated for you shouldn't have an issue tripping or overloading your main.  It is confusing that you can run, say, 450a worth of equipment on a 200a panel but it will almost never draw concurrently at that amperage. 

Extra points for balancing the load across your 3ph service but this gets a little more technical.

[Bearded Lady]

I used to have a 3 phase 220v M&R Fusion, electric dryer.  I don't recall the amperage rating but I remember when my buddy finished getting it hooked up he clamped a meter on the breaker and the amps shot WAY up. it was close to but just under the rating on the serial plate and then it went down to about 60%-70% of that once it hit the the temp setting.