Ambulance Connected to Building Via Cord and Plug

[jvacierto]

I work for an ambulance manufacturer, but I also have 5 years of experience in building electrical systems. Our customers connect their ambulances via cord-and-plug through a shoreline receptacle on the ambulance for battery charging and for power to 125V convenience outlets inside the ambulance. When the ambulance is NOT plugged in and the 125V are no powered, or they are power via an inverter or generator on the ambulance, I understand the 125V electrical system does NOT have to meet NEC, except as required by ambulance codes such as KKK and NFPA.

However, when the ambulance IS plugged in to the building, it is my belief the receptacles in the ambulance are then to be considered plugged into the building electrical system, and therefore the NEC would then have to be applied because of the cord-and-plug nature of the way the ambulance is being connected. Most of our customers use a 20A shoreline, therefore I treat the branch circuit as having a 20A breaker, meaning the 80% maximum amperage rule applies. I have been limiting our customer to having a maximum of 11 receptacles in the ambulance, but I am now getting push back. I have cited the sections in article 210 which show the correct load calculations for receptacles.

So my question is, am I being too strict in my application of the NEC to the cord-and-plug branch circuit feeding the ambulance? There is no local ambulance electrical system authority I can talk to, so it's been hard trying to find a definitive answer to the applicability of the NEC to ambulances.

 

[qcroanoke]

I work for an ambulance manufacturer, but I also have 5 years of experience in building electrical systems. Our customers connect their ambulances via cord-and-plug through a shoreline receptacle on the ambulance for battery charging and for power to 125V convenience outlets inside the ambulance. When the ambulance is NOT plugged in and the 125V are no powered, or they are power via an inverter or generator on the ambulance, I understand the 125V electrical system does NOT have to meet NEC, except as required by ambulance codes such as KKK and NFPA.

However, when the ambulance IS plugged in to the building, it is my belief the receptacles in the ambulance are then to be considered plugged into the building electrical system, and therefore the NEC would then have to be applied because of the cord-and-plug nature of the way the ambulance is being connected. Most of our customers use a 20A shoreline, therefore I treat the branch circuit as having a 20A breaker, meaning the 80% maximum amperage rule applies. I have been limiting our customer to having a maximum of 11 receptacles in the ambulance, but I am now getting push back. I have cited the sections in article 210 which show the correct load calculations for receptacles.

So my question is, am I being too strict in my application of the NEC to the cord-and-plug branch circuit feeding the ambulance? There is no local ambulance electrical system authority I can talk to, so it's been hard trying to find a definitive answer to the applicability of the NEC to ambulances.

I would be more concerned about the onboard inverter or generator being able to supply the load than I would shore power. When it's pluged in to premise wiring it most likely is not being used.

 

[jvacierto]

I would be more concerned about the onboard inverter or generator being able to supply the load than I would shore power. When it's pluged in to premise wiring it most likely is not being used.

Both the other electrical engineer and I are definitely concerned with the onboard inverter or generator. We are already on the border of safety with the (11) 125V outlet maximum limit we have given to sales. However, our ambulance dealers want to put in as many as 15 outlets or more in the ambulances and unfortunately there is no receptacle limit called out in ambulance codes, such as KKK and NFPA. Sales is asking why we can't put in more outlets. Thus, we have to fall back on the NEC, since the inverter usually transfers to the building power when the shoreline is plugged in and we can argue we are trying to protect the cord-and-plug connection from overcurrent from the building.

As for the ambulance not being used when it's plugged in, that's normal, but with ambulances having multiple refrigerators, heaters, 12/125V dual voltage HVAC systems, etc., the electrical load is increasing all the time and the possibility of over current has increased, even with the ambulance sitting idle plugged into the shoreline. I would rather err on the side of caution.

 

[petersonra]

I work for an ambulance manufacturer, but I also have 5 years of experience in building electrical systems. Our customers connect their ambulances via cord-and-plug through a shoreline receptacle on the ambulance for battery charging and for power to 125V convenience outlets inside the ambulance. When the ambulance is NOT plugged in and the 125V are no powered, or they are power via an inverter or generator on the ambulance, I understand the 125V electrical system does NOT have to meet NEC, except as required by ambulance codes such as KKK and NFPA.

However, when the ambulance IS plugged in to the building, it is my belief the receptacles in the ambulance are then to be considered plugged into the building electrical system, and therefore the NEC would then have to be applied because of the cord-and-plug nature of the way the ambulance is being connected. Most of our customers use a 20A shoreline, therefore I treat the branch circuit as having a 20A breaker, meaning the 80% maximum amperage rule applies. I have been limiting our customer to having a maximum of 11 receptacles in the ambulance, but I am now getting push back. I have cited the sections in article 210 which show the correct load calculations for receptacles.

So my question is, am I being too strict in my application of the NEC to the cord-and-plug branch circuit feeding the ambulance? There is no local ambulance electrical system authority I can talk to, so it's been hard trying to find a definitive answer to the applicability of the NEC to ambulances.

I think you are making a couple of mistakes. First off, no where in the code does it require you to limit the number of general purpose receptacles on a branch circuit to 180 VA per circuit. The 180VA number is solely for the purpose of the calculated load. You can put 100 of them on a single circuit if you want to.

Second, take a look at what the code says about vehicles.

90.2 Scope.
(B) Not Covered. This Code does not cover the following:
(1) Installations in ships, watercraft other than floating buildings,
railway rolling stock, aircraft, or automotive vehicles
other than mobile homes and recreational vehicles

I don't see anyway an ambulance qualifies as either a mobile home or an RV so it just is not covered by the NEC because the NEC specifically says so.

 

[jvacierto]

I think you are making a couple of mistakes. First off, no where in the code does it require you to limit the number of general purpose receptacles on a branch circuit to 180 VA per circuit. The 180VA number is solely for the purpose of the calculated load. You can put 100 of them on a single circuit if you want to.

Second, take a look at what the code says about vehicles.


I don't see anyway an ambulance qualifies as either a mobile home or an RV so it just is not covered by the NEC because the NEC specifically says so.

That's exactly the argument the dealers and sales are trying to give us. I totally agree that the vehicle is not covered by the NEC, except for the fact that it is plugged in using a cord-and-plug connection, which is assumed to be fed by a branch circuit from the building. When the inverter transfers power in the ambulance from the inverter to the shoreline input, the ambulance receptacles are essentially directly plugged into the build system thought a cord. This would be like plugging in a power strip into an extension cord, and last I knew you couldn't plug in a 100 outlet power strip into an extension cord, at least not without getting a lot of nuisance tripping of the breaker and a very unhappy client.

So, to be safe and make sure we are not overloading the cord-and-plug, and to meet the 80% rule maximum for branch circuit amperage from the building, we have been using the 180 VA per duplex (or 90 VA per single) receptacle rule of thumb.

Of course, the inverter itself is limited depending on the model (10 amps max, or about 7 amps nominal, for our most used model), so again the "as many outlets as you'd like" seems a bit like giving up, even if the ambulance doesn't technically have to meet NEC. I'd rather be prudent than put in as many outlets as the customer wants and get customer complaints/warranty claims later on due to burned out inverters, melted shoreline cords/plugs, etc., which we have had.

Thanks for the help.

 

[gadfly56]

That's exactly the argument the dealers and sales are trying to give us. I totally agree that the vehicle is not covered by the NEC, except for the fact that it is plugged in using a cord-and-plug connection, which is assumed to be fed by a branch circuit from the building. When the inverter transfers power in the ambulance from the inverter to the shoreline input, the ambulance receptacles are essentially directly plugged into the build system. This would be like plugging in a power strip into a duplex receptacle, and last I know you couldn't plug in a 100 outlet power strip into a duplex receptacle, at least not without getting a lot of nuisance tripping of the breaker and a very unhappy client.

So, to be safe and make sure we are not overloading the cord-and-plug, and to meet the 80% rule maximum for branch circuit amperage from the building, we have been using the 180 VA per duplex (or 90 VA per single) receptacle rule of thumb.

Of course, the inverter itself is limited depending on the model (10 amps max, or about 7 amps nominal, for our most used model), so again the "as many outlets as you'd like" seems a bit like giving up, even if the ambulance doesn't technically have to meet NEC. I'd rather be prudent than put in as many outlets as the customer wants and get customer complaints/warranty claims later on due to burned out inverters, melted shoreline cords/plugs, etc., which we have had.

Thanks for the help.

Are they looking for more receptacles because they want to load them all up, or is it a case of "Gee, I wish I had one more receptacle on the left side/right side/rear/front/inside/outside" sort of deal?

 

[jvacierto]

Are they looking for more receptacles because they want to load them all up, or is it a case of "Gee, I wish I had one more receptacle on the left side/right side/rear/front/inside/outside" sort of deal?

The customers say it's for convenience, but we all know the more receptacles people have, the more they think they can plug in, and they will. For instance, we have customers who have requested 125V medical air compressors, which can draw up to 5 amps at 125V. On a 10 amp inverter, that doesn't leave much room for other equipment they might plug in, so we have to start somewhere with calculating load on the 120V receptacles.

 

[jvacierto]

I work for an ambulance manufacturer, but I also have 5 years of experience in building electrical systems. Our customers connect their ambulances via cord-and-plug through a shoreline receptacle on the ambulance for battery charging and for power to 125V convenience outlets inside the ambulance. When the ambulance is NOT plugged in and the 125V are no powered, or they are power via an inverter or generator on the ambulance, I understand the 125V electrical system does NOT have to meet NEC, except as required by ambulance codes such as KKK and NFPA.

However, when the ambulance IS plugged in to the building, it is my belief the receptacles in the ambulance are then to be considered plugged into the building electrical system, and therefore the NEC would then have to be applied because of the cord-and-plug nature of the way the ambulance is being connected. Most of our customers use a 20A shoreline, therefore I treat the branch circuit as having a 20A breaker, meaning the 80% maximum amperage rule applies. I have been limiting our customer to having a maximum of 11 receptacles in the ambulance, but I am now getting push back. I have cited the sections in article 210 which show the correct load calculations for receptacles.

So my question is, am I being too strict in my application of the NEC to the cord-and-plug branch circuit feeding the ambulance? There is no local ambulance electrical system authority I can talk to, so it's been hard trying to find a definitive answer to the applicability of the NEC to ambulances.

Just to add to the confusion, the codes which govern ambulance electrical systems are KKK and NFPA. These codes reference the NEC when it comes to receptacle placement, grounding practices, and other standards for the 125V system, so even if the ambulance isn't covered by NEC, the codes which cover ambulances refer to the NEC by default.

 

[petersonra]

The customers say it's for convenience, but we all know the more receptacles people have, the more they think they can plug in, and they will. For instance, we have customers who have requested 125V medical air compressors, which can draw up to 5 amps at 125V. On a 10 amp inverter, that doesn't leave much room for other equipment they might plug in, so we have to start somewhere with calculating load on the 120V receptacles.

the only thing that will happen if they overload the circuit is that the CB will trip. it is not like it will be anything other than an inconvenience.

 

[jvacierto]

I think you are making a couple of mistakes. First off, no where in the code does it require you to limit the number of general purpose receptacles on a branch circuit to 180 VA per circuit. The 180VA number is solely for the purpose of the calculated load. You can put 100 of them on a single circuit if you want to.

Second, take a look at what the code says about vehicles.


I don't see anyway an ambulance qualifies as either a mobile home or an RV so it just is not covered by the NEC because the NEC specifically says so.

Just to add to the confusion, the codes which govern ambulance electrical systems are KKK and NFPA. These codes reference the NEC when it comes to receptacle placement, grounding practices, and other standards for the 125V system, so even if the ambulance isn't covered by NEC, the codes which cover ambulances refer to the NEC by default.

 

[jvacierto]

the only thing that will happen if they overload the circuit is that the CB will trip. it is not like it will be anything other than an inconvenience.

That's for sure, it will be inconvenient for the dealer when the customer complains, then inconvenient for us when the dealer complains to our warranty/service department, then inconvenient for me and the other electrical engineer when we are asked why we didn't let the customer know about the nuisance tripping. Sorry to get sarcastic, just been there done that.

 

[petersonra]

That's for sure, it will be inconvenient for the dealer when the customer complains, then inconvenient for us when the dealer complains to our warranty/service department, then inconvenient for me and the other electrical engineer when we are asked why we didn't let the customer know about the nuisance tripping. Sorry to get sarcastic, just been there done that.

people make all kinds of bad decisions when they buy stuff and don't get what actually meets their needs. That is not the fault of the designer. it is the fault of the guy that bought it for not buying what he actually needed.

if you were to break it up into 2 120V branch circuits inside the ambulance, how would you prevent them from plugging it into the same 8A invertor, or into two receptacles that are on the same circuit?

 

[ron]

My refrigerator or my relocatable power tap (power strip) does not comply with the NEC, they have their own UL standards to follow.

Similar for the ambulance.

The worst that will happen is the breaker will trip.

 

[don_resqcapt19]

the only thing that will happen if they overload the circuit is that the CB will trip. it is not like it will be anything other than an inconvenience.

I can see it being a lot more than an inconvenience if the breaker trips while electrical equipment is being used for patient care.

 

[growler]

I can see it being a lot more than an inconvenience if the breaker trips while electrical equipment is being used for patient care.

So can I but I think I would start with a bigger inverter. Then maybe seperate circuits for critical and noncritical use. The AC going out probably won't kill you.

 

[infinity]

Unless there were a way to limit the load on all 11 receptacles to stay below 20 amps the number of receptacles is irrelevant. I could easily overload a 20 amp circuit with a single duplex receptacle connected to it.

 

[qcroanoke]

I can see it being a lot more than an inconvenience if the breaker trips while electrical equipment is being used for patient care.

especially if it's being used on me!!

 

[jim dungar]

I totally agree that the vehicle is not covered by the NEC, except for the fact that it is plugged in using a cord-and-plug connection, which is assumed to be fed by a branch circuit from the building.

The NEC ends at the outlet. Effectively your ambulance is simply end use equipment, like a appliance.
You rationale of 'it is plugged therefore the NEC applies' goes completely against many code sections, in particular 110.3(B) and 110.26. Is your ambulance Listed or Labeled? Do you maintain 30" of width in front of electrical equipment that needs servicing like your inverters.

 

[mgookin]

The NEC ends at the outlet. Effectively your ambulance is simply end use equipment, like a appliance.
You rationale of 'it is plugged therefore the NEC applies' goes completely against many code sections, in particular 110.3(B) and 110.26. Is your ambulance Listed or Labeled? Do you maintain 30" of width in front of electrical equipment that needs servicing like your inverters.

Absent anything to the contrary, the NEC ends at the outlet.
OP has a national standard that says when the ambo is plugged in, it must meet NEC. But let's put that aside.

OP is building ambulances. He wants to build a good ambulance. He only has 20A 120V to work with. His marketing dep't is throwing him under the bus (no pun intended). How can we help this man build an ambulance which will not be experiencing electrical system failure? Should we advise him to provide a bigger service? Is that possible? Does every ER in the nation have a single 120V 20A connection? Or is it industry standard to have ganged 120V 20A connections such that OP can build a better ambo by having multiple connections?

As technology advances these ambos are going to be filled with more and more technology. Add to that the employees working in there are charging their phones, and probably the patients too. Not that the phones take power but they take receptacles and that's one of the issues on the table.

An ambulance with a failed electrical system becomes a hearse!

 

[iwire]

So my question is, am I being too strict in my application of the NEC to the cord-and-plug branch circuit feeding the ambulance?

Yes.

The NEC does not apply to the ambulance regardless of it being connected to shore power

Same for watercraft or appliances.

Just because you wire up a listed appliance to a building does not mean the NEC applies to the internal wiring.