Ambulance Connected to Building Via Cord and Plug

[GeorgeB]

The main problem is the fact that customers are asking for more outlets than we are comfortable giving them.

Have you considered a meter for current? I wonder how many of those outlets are used for cell phone or radio chargers?

 

[jvacierto]

Actully those sections support the consensus that the NEC does not apply except the sections specifically called out by the documents you posted.

I understand, your heart is in the right place, you are trying to make do a quality job.

But we can't make the NEC apply where it does not.

I hate to use the term slippery slope, but that's exactly what I was afraid of, and that's the interpretation of sales and the dealers. If it's not specifically prevented by code, then we should be able to do anything we want. We have had ambulances burn down due to electrical issues and we were not able to pinpoint exactly what caused the fires other than "electrical issues." So I'm sure everyone can understand why I'm trying to be as cautious as possible. The NEC is the code I know of that gives a conservative way of calculating receptacle loads.

Thanks to everyone for the feedback.

 

[jvacierto]

So the problems is sales VS engineering.

The sales dept. wants more receptacles because that's more money (makes the customer happy) and engineering thinks that may cause problems. Sound more like a design issue than a code issue.

I would try to collect data from within the industry. There is competition, so what are the other guys doing and how have they solved the problem?

We are trying to collect data, but it's hard finding that information. I thought I'd post on this forum to get some thoughts from engineers who were more versed in the NEC compared to engineers in the ambulance industry. I have 5 years in the achitecture/engineering industry, but I left that industry about 6 years ago, so this has been a good exercise in catching up on the NEC.

 

[jvacierto]

That's a very common problem across many industries.

Sales and marketing want to sell what does not exist, then the engineers need to make it happen. And if it doesn't work, who do you think gets blamed? OP gets thrown under the bus (no pun intended)

It seems like we get thrown under the bus either way, so we might as well get thrown under fighting.

 

[jvacierto]

hmy:

We are derailing the OPs thread by talking about the OPs question?



As far as your own question about how we can help build a better ambulance I don't think we can. We are not signing the checks.

We see other competitor's ambulances every year at an annual show for fire rescuers, so there's definitely room to build a better ambulance.

As for derailing from my original post, I apologize, I probably am conflating the code question with the quality issues we are trying to solve. I just can't help but have the public's safety as my first priority in the design. Public safety/care Is why the ambulance industry exists.

 

[winnie]

Many of the discussions on this board revolve around just exactly what the code rules mean. In your case it seems that you are more interested in what approximate guidance code can provide for your discussions with sales.

My opinion: as far as the NEC is concerned, your ambulance is an appliance that gets plugged in. IMHO the combination of NEC rules and UL standards will limit the amount of power that may be supplied via a single cord and plug connection, but the NEC does not limit the number of receptacles inside of the ambulance.

The '180 VA per yoke' used for calculating loads on circuits (in some situations only) is vaguely useful guidance, but your experience with the actual loads that your customers use is probably much better guidance.

I'd suggest, (totally off base given my lack of experience in the field) letting the customer having as many receptacles as they want, but wired in such a fashion as to permit easy upgrades, for example using multiple home runs so that circuits can be split and supplied with 2 inverters, or wiring using x-3 cable to permit upgrade to a 120/240V inverter and MWBCs. Make it up to sales to warn the customer that no matter how many receptacles they have, they can only use xxx amount of power, and then when the customer finds that they need more make it an easy up-sell

-Jon

 

[mgookin]

OP:
What is the output on the genset?
What is the shore connection?

If you could have anything you wanted and it cost nothing, what would you have for power available?

 

[Strathead]

We see other competitor's ambulances every year at an annual show for fire rescuers, so there's definitely room to build a better ambulance.

As for derailing from my original post, I apologize, I probably am conflating the code question with the quality issues we are trying to solve. I just can't help but have the public's safety as my first priority in the design. Public safety/care Is why the ambulance industry exists.

One thing that was mentioned very early on and then, I think, distorted by you is that the code doesn't limit the number of receptacles on a circuit. One person stated you can put 100 duplexes on one circuit if you wish. To which you replied that you know you CAN"T put a 100 plug strip on a circuit, but you can.

Yes you are conflating code with quality, and the code is not only not applicable it doesn't specifically prohibit the practice. If your genuine concern is that the load of the ambulance may exceed the safe value when plugged in then limiting it is very simple. First thing I wonder is what is the plug configuration of the cord cap on the ambulance. If it is a NEMA 5-15P then you can start right there. Next you can ensure that the first device after the plug is a 20A fuse or breaker. When a customer wants more capacity you can offer a larger feed similar to an RV with a 240 volt 30A system for example.

I just think you need to stop trying to use the NEC to justify your concerns. You are an engineer, you should be fully capable of baffling them with math if you need to. You don't need to fight fair.

 

[K8MHZ]

Ambulances are not and should not be covered by the NEC. Using the NEC as a design manual for ambulances is neither prudent nor safe.

Chapter 3 wiring should not be used. Automotive and marine wiring is made to be flexible, sustain vibration and has insulation designed to be used without a raceway. Solid conductor wiring should NEVER be used. Certain insulation types should never be used.

Obviously, an ambulance won't have an earth grounding electrode.

Automotive wire diameter seems too small by NEC standards. Usually at least by 2 AWG sizes.

What needs to be considered is the load that will be used, not the number of receptacles. If the load will be no more than 10 amps on a 20 amp inverter, what harm would it be to have 50 receptacles?

If the customer has the need to plug 25 devices in, they will do it, regardless the number of installed receptacles, so you may as well give them what they want. If you think that more receptacles will equate to more load, then both the shore power source and inverter will need to be upsized, and limiting receptacles won't affect that. One could plug two 1500 watt space heaters into a single receptacle and overload a 20 amp circuit.