The most common mistake is sizing to the running amps on the nameplate and ignoring what the equipment draws when it starts. Floor grinders and dust collectors both pull more current for a moment at startup than they do while running, and a generator sized without that margin can sag, trip or stall the tool. The other mistakes on this page share a root: the load list was built from memory instead of from the equipment actually on site.
Dust control is the reason the dust collector load cannot be treated as optional. OSHA’s 1926.1153 silica standard calls for dust collection or water delivery when grinding concrete, so a collector that loses power can stop the job. Sizing the generator for the grinder alone and adding the collector later is a way to find that out in the middle of a shift. The cost of a collector dropping out mid-pass is covered in what a power dip costs on a polished concrete job.
Mistake 1: Counting running amps only
A nameplate gives running current, but motors draw a higher surge when they start. If the generator has no headroom for the largest startup load, the voltage can dip as the motor turns, and the tool may stall or the generator may shut down. Startup draw varies by motor and equipment, so check the figures for your own machines instead of using a rule of thumb. The amperage chart helps convert between kW and amps for the unit you are considering.
Mistake 2: Leaving the dust collector off the list
On a prep job, the grinder and the collector run together, and the collector often has its own motor and startup draw. Build the list around the whole system, with the grinder, the collector, any vacuum and the lights. Then check which items start at the same time and which can be staggered. Staggering startups is a free way to reduce the peak the generator has to handle.
Mistake 3: Adding up everything the crew owns
A list of every tool in the truck produces a total larger than any real shift. Tools that never run together do not stack, so the sum overstates the need and leads to a bigger, costlier unit. The goal is the simultaneous load, which is what the crew runs at once plus the largest startup. The construction generator sizing guide walks through that approach.
Mistake 4: Ignoring voltage, phase and cable length
A tool built for one voltage or phase will not run properly on another, and a long cable run can drop voltage at the far end. Check the plate on each machine and confirm the generator’s voltage and phase before the unit ships. Then look at the distance from the generator to the work. The power calculator can help with the load side of that check. If the GC is expected to supply the power, who supplies power on a prep subcontract explains why capacity, voltage and phase should be confirmed before the bid.
What the mistakes look like in the field
The table below pairs each mistake with the symptom a crew would notice and the habit that prevents it. It is a checklist for the planning stage, not a diagnosis tool, since the same symptom can have several causes.
| Mistake | Symptom on site | Habit that prevents it |
|---|---|---|
| Running amps only | Tool stalls or generator trips at startup | Add the largest startup load to the list |
| Collector left off | Work stops when the collector cannot run | List the whole grinding system together |
| Counting every tool | Oversized, costly unit | Total the simultaneous load only |
| Wrong voltage, phase or long runs | Tools run poorly or not at all | Check plates and plan cable distances |
What to do before the rental arrives
The list below is a short routine that catches most of these mistakes before the unit is delivered. It takes a few minutes and uses information the crew already has.
- Write down every machine that will run, with voltage, phase and amps
- Mark which machines start together and which can be staggered
- Add the largest startup load to the simultaneous total
- Confirm the generator’s voltage and phase match the equipment
- Note the cable distance from the unit to the work
For a broader look at powering a grinding crew, see our page on concrete surface prep power.
Getting the size right with Stag
Stag Power Rentals supplies diesel generators from 20 kW to 2000 kW out of its Dickinson, TX yard. Send the equipment list and the team can help check it against a size class before the unit ships. For the wider picture, see our construction power overview, and when your list is ready, request a quote.
Frequently Asked Questions
Why does my grinder stall when the generator is big enough on paper?
A generator can have enough running capacity and still struggle at startup, when motors draw a surge. Voltage can dip as the motor turns. Adding the largest startup load to your list, and staggering startups, can help.
Do I need to include the dust collector when sizing?
Yes. The collector is part of the grinding system and runs at the same time. Leaving it off can leave the generator short and can stop work when dust control is required.
Is it better to oversize the generator to be safe?
Not necessarily. An oversized unit costs more and may run at a light load much of the time. A list based on simultaneous load, with startup headroom, usually gives a better fit.
How do I check voltage and phase for my equipment?
Read the plate on each machine and match it to the generator’s output. Confirm before the unit ships, since a mismatch can stop work on arrival.
What should I send with a quote request?
Send the equipment list with voltage, phase and amps, the expected run hours, and the cable distance from the unit to the work. Mention which machines run together. That lets the rental team size the unit in one pass.