Quick question for the crew here! do you guys recommend surge protection between a generator and the main panel, or do you consider it overkill? I’ve had a couple of callbacks lately where customers had weird voltage spikes when power flipped back from utility to gen or vice versa. Some setups have SPDs on both ends, but I’ve also heard that stacking them can cause more harm than good if they’re not rated right. Curious what setups have actually worked best for you all. Do you install surge protection as standard, or just rely on a solid transfer switch and grounding?
Surge protection between gen and panel necessary or not?
- Thread starter GreyFox
- Start date
Hi GreyFox,
My generator work is usually three phase, megawatt or more units at voltages from 120/208 to typically13,200, so my experience with single phase generators or any small kW units is limited to project or client add-ons & some family-friend freebies. (Houses usually for family/friend)
On those small unit jobs that I have done or serviced, I noticed that the alternator's output typically becomes stable before the unit transfers. (GE units seem to excel at this task).
Some voltage dip might occur when a bunch of stuff starts at once if the generator is sized close to load. (For example, if the load switches while an air conditioner or electric oven is heating and many lamps are on.)
The Trouble Spot:
When the utility re-energizes, there often is a rather lengthy voltage drop until everyones' items start up and the supplied voltage stabilizes. A surge suppressor won't help with that. (See the last paragraph for a solution)
Unfortunately, often after the initial load stabilized, the recovery results in a spike over voltage. That is when a surge suppressor would be helpful.
Perhaps that is what your clients are noticing.
Of course, if the generator set's voltage regulator isn't working well, spikes can happen.
The solution I employ for 'critical voltage & frequency' loads is a rectifier-inverter system with storage in between. This ensures no voltage drop or spike. (Sometimes I will employ a true "generator" which produces DC instead of an alternator & engine which we call a "generator"..)
Unfortunately, this rectifier-inverter set up is possibly quite expensive for a home or small commercial venue. But, I may be wrong about cost. It might be worth checking into pricing.
Just some ideas to consider,
Paul
My generator work is usually three phase, megawatt or more units at voltages from 120/208 to typically13,200, so my experience with single phase generators or any small kW units is limited to project or client add-ons & some family-friend freebies. (Houses usually for family/friend)
On those small unit jobs that I have done or serviced, I noticed that the alternator's output typically becomes stable before the unit transfers. (GE units seem to excel at this task).
Some voltage dip might occur when a bunch of stuff starts at once if the generator is sized close to load. (For example, if the load switches while an air conditioner or electric oven is heating and many lamps are on.)
The Trouble Spot:
When the utility re-energizes, there often is a rather lengthy voltage drop until everyones' items start up and the supplied voltage stabilizes. A surge suppressor won't help with that. (See the last paragraph for a solution)
Unfortunately, often after the initial load stabilized, the recovery results in a spike over voltage. That is when a surge suppressor would be helpful.
Perhaps that is what your clients are noticing.
Of course, if the generator set's voltage regulator isn't working well, spikes can happen.
The solution I employ for 'critical voltage & frequency' loads is a rectifier-inverter system with storage in between. This ensures no voltage drop or spike. (Sometimes I will employ a true "generator" which produces DC instead of an alternator & engine which we call a "generator"..)
Unfortunately, this rectifier-inverter set up is possibly quite expensive for a home or small commercial venue. But, I may be wrong about cost. It might be worth checking into pricing.
Just some ideas to consider,
Paul
- Joined
- Feb 21, 2025
- Messages
- 184
A lot of folks lean on the transfer switch to handle most of the messy handoff, but those voltage bumps during the changeover can definitely justify an SPD if the setup isn’t rock solid. The trick is matching the ratings so the devices aren’t fighting each other. On the callbacks you mentioned, were the spikes happening during transfer or after the generator settled in?
Loto_Arusu
Member
- Joined
- Oct 5, 2025
- Messages
- 6
I wouldn’t call it overkill, but stacking SPDs without checking ratings is definitely asking for weird behavior. I’ve seen guys throw in cheap Type 2s everywhere like it’s seasoning salt. If the gen is portable and the transfer switch is decent, the panel SPD is what really matters.
Loto_Arusu cautioned against stacking Surge Protection Devices. If that refers to putting them in series- absolutely do not do that close-coupled.
I've seen, on lab bench testing, SPDs in series the first in line will hand off the over-voltage that it cannot handle to the second, but multiplied! It is best to obtain the proper capacity device as one unit.
If there is a fair amount of capacitance between the devices, such as one SPD at the generator and one at the other end of a long cord to the load, that will be usually OK. (The cord provides the capacitance.)
It's like having a surge protector at the main service and a plug-in one at a computer or television. The capacitance of the wire in between cures the series-multiplication problem.
OR-
You can parallel the devices and send them to different loads. That causes no problems.
Example: One 15 amp circuit with 3 receptacle outlets. Each outlet has a surge protector plugged into it. One serves a TV, one a computer and one a modem. This is OK to do- even with a whole building surge device at the load center ahead of them.
Paul
PS: There is always a surge protection device ahead of what you are powering. When I was a linesman, we had them on some transformers where the secondary was 13,200 volts for distribution. They were also on some low voltage secondaries, too. Back then, they were big, clunky devices. The generating plant also has them on the primaries.
I've seen, on lab bench testing, SPDs in series the first in line will hand off the over-voltage that it cannot handle to the second, but multiplied! It is best to obtain the proper capacity device as one unit.
If there is a fair amount of capacitance between the devices, such as one SPD at the generator and one at the other end of a long cord to the load, that will be usually OK. (The cord provides the capacitance.)
It's like having a surge protector at the main service and a plug-in one at a computer or television. The capacitance of the wire in between cures the series-multiplication problem.
OR-
You can parallel the devices and send them to different loads. That causes no problems.
Example: One 15 amp circuit with 3 receptacle outlets. Each outlet has a surge protector plugged into it. One serves a TV, one a computer and one a modem. This is OK to do- even with a whole building surge device at the load center ahead of them.
Paul
PS: There is always a surge protection device ahead of what you are powering. When I was a linesman, we had them on some transformers where the secondary was 13,200 volts for distribution. They were also on some low voltage secondaries, too. Back then, they were big, clunky devices. The generating plant also has them on the primaries.
