At a glance
| Buyer | Aerospace manufacturing and test facility, coastal site |
| Project | Outdoor 500kW standby |
| Requirement | 500kW, 480V three phase, fast turnaround |
| Site condition | Salt air, corrosion treatment planned through the buyer’s own coatings vendor |
| Space available | Under 25 feet in length |
| Purchased | New Cummins 500kW, $130,000 |
| Availability | New unit could be on a truck the next day |
The call
It opened the way the good ones do, with somebody who already knew what he needed. 500kW, 480V three phase, and a timeline that was already tight. What he wanted to know first was simply what we had on hand.
We had a straight answer. Several brand new Cummins units sitting in the yard, one of which could be on a truck the following morning.
His very next question is the one this whole article is about, and it is not the question most callers ask second. Did the units already have corrosion treatment on them?
They did not. Not ours, not anybody’s, and our sales engineer said so immediately, along with the part that mattered most which is that corrosion treatment is work done on site, not something that arrives with the machine. The buyer already had a coatings company lined up for it.
The response to that was what made the rest of the call easy. Our engineer told him his own contractor would almost certainly do that work better than anything we could assemble for it.
Nobody ships a corrosion treated generator, and that is the correct answer
Buyers siting equipment near saltwater assume, reasonably, that a manufacturer selling into coastal markets would offer a coastal build. Some of that exists. Cummins, for example, will build enclosures in aluminum rather than steel, and their published enclosure literature names aluminum as the preferred choice in coastal regions and other environments where corrosion is a concern. Standard enclosures are 12 and 14 gauge steel with stainless hardware.
But a factory material choice is not corrosion treatment, and it is a decision made at build time. It is not available on a machine already sitting in a yard, which is exactly the machine a buyer on a compressed schedule needs.
Real corrosion protection in a marine atmosphere is a coatings job, and coatings are their own trade. The reference framework is ISO 12944, which classifies atmospheric corrosivity from C1 for dry heated interiors up to CX for offshore. Coastal sites with high salinity land in C5.
Worth knowing if you are reading older specs: the 2018 revision folded the previous C5-I and C5-M categories into a single C5 for onshore environments and added CX for offshore, so a spec written before 2018 and one written after will use different language for the same site.
Getting a steel enclosure to survive a C5 atmosphere means surface preparation, a zinc rich or epoxy primer, and a topcoat system specified for the exposure, applied by an applicator who does that work every day. A generator dealer that offered to do it in-house would be doing it worse than the coatings contractor already working on that customer’s site. The honest move is to say so.
What actually corrodes, in rough order of how much it will cost you:
Electrical terminations first. Corroded connections raise contact resistance, and contact resistance turns into heat, arcing, and eventually a failure to start when the utility drops. This is the one that ends outages badly.
Then the radiator core, where salt laden air is being pulled through fins continuously by design.
Then exhaust components, which cycle hot and cold and shed protective oxide layers as they do it.
Then the enclosure panels and fasteners, which is what everybody looks at and photographs, and which is genuinely the least urgent of the four.
When to do the work matters as much as who does it. Treat the unit after it is delivered and before it is set, wired, and piped. Every surface is still reachable. Once the machine is on a pad with conduit landed, exhaust connected, and a fuel line run, half of what you wanted to coat is behind something else. On this project the pad had not been poured yet, which meant the buyer had the whole sequence available to him. Most callers do not.
The condition of the metal is part of the purchase decision
Here is the part of the corrosion conversation that changes what you buy rather than what you do after you buy.
If you are going to put a coating system on a generator enclosure, you are buying a substrate. Factory paint on a zero hour machine is intact, uniform, and clean, which is close to ideal for a primer. An eleven year old enclosure that has been outdoors somewhere is a different job. It may be perfectly sound, and often is, but the applicator has to inspect it, address any surface rust, and prepare a surface that has already weathered. That is real labor, and it lands on a line item that did not exist in the price comparison the buyer was running.
In a dry inland environment this does not come up. Nobody coats a genset in Colorado. In a C5 atmosphere it is part of the arithmetic, and it moves the new versus used comparison in a direction most people do not account for.
None of which means used is wrong on the coast. It means the coating cost is not a constant across the options, and a buyer comparing list prices alone is comparing the wrong numbers.
What was actually on the table
The buyer was open to used from the start, and said so plainly. He was on our inventory pages during the call, reading unit numbers off the screen. He was not shopping a category, he was shopping specific machines.
| Build | Hours | Sound attenuation | Price | |
|---|---|---|---|---|
| New Cummins 500kW | Current | 0 | Enclosed | $130,000 |
| Used Kohler 500kW | Used | 360 | None | $95,000 |
| Used MTU 500kW | Newer build, low hours | Low | Level 1 | $90,000 |
| Used MTU 500kW | 2008 | 255 | Level 1 | $75,000 |
His reaction to the first used option was the reaction most people have. If the savings were real he did not mind the hours, so long as there were not too many of them, and 360 struck him as reasonable.
He is right. It is not too big of a deal. A standby generator runs at a constant 1800 RPM under stable load for a few dozen hours a year. 360 hours is a machine that has been started and exercised regularly for a decade, not a machine that has worked.
The catch on that one was sound. It was not attenuated at all, and the buyer’s next question was whether we had anything with at least a Level 1 enclosure. We did, two of them, at $90,000 and $75,000.
So the spread on the table was $130,000 at the top and $75,000 at the bottom.
Why the new unit won
Schedule. The buyer named it twice, and the second time he named it as the deciding factor. Turnaround and shipping were the priority, ahead of price. A new unit in stock ships tomorrow.
The coating job. New paint, zero hours, no weathering. The cheapest surface for a coatings contractor to work with, and on this site the coatings contractor was coming either way.
Sound attenuation without a hunt. The cheapest option with no enclosure treatment was out on those grounds alone.
Add those up and the premium buys a machine that arrives faster, coats cheaper, and needs nothing chased down. At a rating where we stock new, that is frequently how it lands.
The 20 foot problem, and the hoods nobody thinks about
The other half of the call was physical, and it produced the most useful thing in this piece for anyone speccing an outdoor pad.
The buyer’s constraint was twenty feet of length, and he offered it tentatively, as something he was working toward rather than something he had confirmed.
Enclosed 500kW sets commonly run into the high teens and low twenties of feet. A meaningful part of that length on many units is the intake and expulsion hoods, the housings on top that pull air in one end and push it out the other. Two things about them:
They are up off the ground. If the limit is the concrete pad, the hoods overhang it and the pad dimension is not the number that matters. If the limit is a wall or a hard vertical obstruction, the hoods are in the way and the length is real.
They can usually be removed. Which shortens the unit. But not unconditionally, and our engineer flagged the condition before the buyer thought to ask: there have to be protective louvers behind the hood. Typically there are, because the hood is drawing air from above through an opening that already has louvers behind it. Not always. Pull a hood off a unit that does not have them and you have left an opening into the enclosure, which on a coastal site is a considerably worse problem than being nineteen inches too long.
The buyer measured while they were on the phone and came back with about 23 feet available, and correctly downgraded the twenty foot figure from a requirement to a preference.
The practical version of all this, for anyone about to pour a pad:
- Ask for as-is overall dimensions and hood-removed dimensions as two separate numbers. Most listings publish one of them.
- Say whether your limit is the pad or an obstruction. They are different constraints and only one of them is blocked by a hood.
- Confirm louvers behind any hood before planning to remove it.
- Pick the machine before you pour. This buyer had that option and it is worth more than it sounds. Concrete is the one part of a generator project that cannot be adjusted afterward.
Sound attenuation at 500kW: your choice is Level 1 or Level 2
Since the buyer’s floor was a Level 1 enclosure, worth being precise about what the levels are and are not.
Enclosure levels describe noise emissions and are an industry convention rather than a code. On Cummins packages, Level I generally runs 70 to 89 dB(A) and Level II 63 to 78 dB(A), measured at full load, 7 meters from the source, on steel enclosures. The physical difference is largely acoustic foam added to doors and interior panels, which means Level 2 performance is frequently reachable as a retrofit rather than something you have to find on the used market and wait for.
You will also see a Level III figure of 68 to 70 dB(A) published. Read the footnote: Cummins offers Level III only on diesel models from 100 to 150kW. It is not an option at 500kW, which is why the number looks like it undercuts Level II. At this rating the real menu is Level I, Level II, or a purpose built acoustic structure.
Two things worth carrying into any spec:
A dB(A) number without a measurement distance is not a number. Ratings are stated at a set distance, commonly 7 meters or 23 feet. Comparing across distances tells you nothing.
Enclosure Level 2 and NFPA 110 Level 2 are unrelated. Enclosure levels describe sound. NFPA 110 Levels 1 and 2 classify emergency power supply systems by consequence of failure, with Level 1 where failure could cause loss of life or serious injury. They share a number and nothing else.
Why a 2008 machine is still a legal standby unit
The $75,000 option was a 2008 build, and buyers reasonably ask whether a pre-Tier 4 engine can still be permitted.
For emergency standby, usually yes, and the reason is structural rather than a loophole. Under EPA’s NSPS Subpart IIII, emergency stationary compression ignition engines are held to standards based on the earlier nonroad tiers and are specifically excluded from the requirements that would force add-on controls such as diesel particulate filters or NOx reduction catalysts. Emergency engines are also limited to 100 hours per year for maintenance and readiness testing, which is the tradeoff for the relief.
That single provision is most of why the used market at this size is worth shopping. A standby machine built before Tier 4 Final is not an orphan asset, it is a compliant one, and it does not carry the aftertreatment that makes a new nonroad-tiered engine more expensive to buy and more complicated to maintain.
The caution: federal is the floor. State and local air authorities can and do impose their own permitting requirements on stationary engines, and those vary considerably by state and sometimes by county. Confirm with the permitting authority for the site before you buy on emissions grounds, not after.
Where the machine sits is part of what it costs
One of the units the buyer liked was in our Jacksonville, Florida yard. That is a real distance to the western Gulf Coast, and it shows up twice, once in the freight number and once in the calendar.
At 500kW and up, price the unit and the freight as one figure. A cheaper machine two states away is frequently not cheaper, and if the project is against a date, the schedule cost is larger than the freight cost. It is the reason we run yards in Brighton CO, Jacksonville FL, Pensacola FL, and Austin TX rather than one central warehouse.
On this project it was less about dollars than days. The buyer had named turnaround as the priority. The new unit was ready to load the following morning. That is difficult to compete with.
What buyers should take from this
- No generator ships corrosion treated. Coastal protection is a coatings job done on site, by a coatings contractor, and a dealer telling you otherwise is selling you something they do not do well.
- Treat the unit before it is set and connected. Once conduit, exhaust, and fuel are attached, the surfaces you wanted to coat are behind something.
- Protect the electrical terminations first. Corroded connections raise contact resistance, and that is what turns a corrosion problem into a failure to start.
- On the coast, the condition of the enclosure is part of the price. Prepping a weathered surface for a coating system is labor that does not appear in a list price comparison.
- Aluminum enclosures exist for coastal sites, but they are a factory build decision. They are not available on a unit that has to ship this week.
- Ask why your length limit is your length limit. A pad constraint and a wall constraint are different problems, and only one of them is affected by removable hoods.
- Confirm louvers before removing a hood. Shortening a machine by opening a hole in it is a bad trade anywhere and a terrible one near salt air.
- Pick the machine before you pour the pad. It is the only part of the project you cannot revise later.
- At 500kW your sound options are Level 1 and Level 2. Level III is a 100-150kW offering, whatever the chart implies.
- Emergency standby engines are exempt from Tier 4 add-on controls, within 100 hours per year. Confirm state and local permitting separately.
Frequently asked questions
Do generators come with corrosion protection for coastal environments? Not as a standard feature. Manufacturers offer material choices that help, such as aluminum enclosures in place of steel, which Cummins names as the preferred option in coastal regions, but those are decisions made when the unit is built and are not available on stock inventory. Genuine marine grade corrosion protection is a coating system specified for the site’s corrosivity category and applied by a coatings contractor, normally after delivery and before the unit is set and connected.
What is the ISO 12944 corrosivity category for a coastal site? Coastal and high salinity onshore environments generally fall under C5, described as very high corrosivity. Offshore and extreme conditions fall under CX, a category added in the 2018 revision of the standard. That revision also replaced the older C5-I and C5-M designations with a single C5 for onshore use, so specifications written before and after 2018 describe the same environment differently.
When should a generator be corrosion treated, before or after installation? After delivery and before installation. Every surface on the machine is accessible at that point. Once the unit is set on its pad with conduit, exhaust, and fuel connections made, a significant portion of what needs coating is obstructed, and the work becomes more expensive and less complete.
What parts of a generator corrode first in salt air? Electrical terminations are the highest consequence. Corroded connections increase contact resistance, which produces heat, arcing, and ultimately a failure to start when the unit is called. Radiator cores are next, because salt laden air is drawn through them continuously by design, followed by exhaust components that cycle hot and cold, and finally enclosure panels and hardware, which are the most visible and the least urgent.
How long is a 500kW generator? Enclosed 500kW sets commonly fall in the high teens to low twenties of feet, and the figure varies by manufacturer and enclosure package. Intake and expulsion hoods account for a meaningful portion of the overall length on many units. Always request as-is and hood-removed dimensions as separate numbers when space is a constraint.
Can you remove the hoods from a generator enclosure to make it fit? Frequently, yes. Intake and expulsion hoods sit above the enclosure and can often be taken off to reduce overall length, but only if protective louvers exist behind them. Without louvers, removing a hood leaves an opening into the enclosure, which is a serious problem in a corrosive or wet environment. Confirm before planning around it. Note also that hoods sit above pad level, so if the constraint is pad size rather than a wall, they may not affect fit at all.
Is there a Level 3 sound attenuated enclosure for a 500kW generator? Not from Cummins. Level III packages, published at 68 to 70 dB(A), are offered only on diesel models from 100 to 150kW. At 500kW the practical options are Level I, generally 70 to 89 dB(A), and Level II, generally 63 to 78 dB(A), or a separately engineered acoustic structure. Always confirm the measurement distance attached to any dB(A) figure, commonly 7 meters or 23 feet.
Can you still install a pre-Tier 4 generator for standby power? In most cases yes. EPA’s NSPS Subpart IIII holds emergency stationary compression ignition engines to standards based on earlier nonroad tiers and specifically excludes requirements that would necessitate add-on controls such as diesel particulate filters or NOx reduction catalysts. Emergency engines are limited to 100 hours per year for maintenance and readiness testing. State and local air permitting authorities may impose additional requirements, so confirm for the specific site.
Is 360 hours a lot for a used generator? No. Standby generators run at a constant 1800 RPM under stable load for a few dozen hours per year, mostly weekly exercise cycles. A unit with 360 hours has been started and exercised regularly over many years rather than worked, and industrial sets in this class remain serviceable well beyond 10,000 hours.
How much does a 500kW standby generator cost? A new Cummins 500kW sold for $130,000 in this case. Comparable used 500kW units in inventory at the same time listed at $75,000 for a 2008 build with 255 hours, $90,000 for a newer sound attenuated unit, and $95,000 for a 360 hour unit without sound attenuation. None of those figures include freight, the concrete pad, transfer equipment, installation, or corrosion treatment.
Speccing standby power for a corrosive site
Generator Source is the largest buyer and seller of new and used industrial generators in North America, with inventory from 20kW to 4MW+ and branches in Brighton CO, Jacksonville FL, Pensacola FL, and Austin TX. We stock new units at common ratings alongside used inventory, we publish full dimensions, and we will tell you when the work belongs to somebody else.
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