Calculating existing loads on panelboards

Make load flow study ,before adding any new loads to the system.I am sending a brief write up to your email box.after studying ,if you have any doubts please contact.send me your email id to send write up on load flow study.

This forum is mainly for professionals ,who exchange their views/doubts over here.

This is not a place for scam.I am sorry note your comment.In the interest of helping you I have offered to send you the brief note on system study,load flow study.

Thanks for the advice, I've now signed up officially. Please do send over the file, I'd really like to read it.

The rules differ depending on the jurisdiction of the jobsite. In the US, Article 220 of the National Electric Code give calculation methods for various types of occupancy. There are tables & formulae to determine lighting load based on area, and guidance for other types of load, such as air conditioning, appliances, signs, receptacles, etc.

Section 220.16 specifically applies to additions to existing installations.

I looked at 220.16, but that addresses your new loads that will be added to the existing service if I read it correctly.

My question is how to go about determining the existing load - what is currently installed and operating on any given panelboard.

You need to take an overview of the existing installation. Does it look like a "typical" example of what you'd expect to see in the majority of similar situations? If so, use 220.12 & 220.14 to determine general requirements.

For example: Let's say you are renovating a 5000 square foot restaurant for a new tenant.

Step 1: Table 220.12 lists restaurants has needing 2 VA per square foot. 5000 x 2 = 10 KVA for lighting

Step 2: 220.14 covers other specific loads and refers to other articles where those loads are covered. 220.14(B) covers cooking appliances, & refers to 220.55. For other than dwelling units, use Table 220.56. If the kitchen has 3 identical 7500 watt ovens, the demand factor is listed as 90%. 7500 x 3 x 0.9 = 20.25 KVA (since the oven elements are purely resisitive, KW=KVA). Repeat this step for all cooking appliances.

Step 3: 220.14(C) covers HVAC, exhaust fans, refrigerators/freezers, elevators & other motor loads. For HVAC & refrigerators we go to 440.6. We have 2 HVAC units with nameplate ratings of 22 amperes @ 240 VAC. 2 x 22 x 220 = 10.56 KVA. Repeat this step for all major motor loads.

Step 4: 220.14(I) gives a flat value of 180 VA per duplex receptacle. Our restaurant has 25 duplex receptacles scattered through the premises. 25 x 180 = 4.5 KVA.

Add up the KVA totals from each step to get the total for the premises. If you are only concerned with a particular sub-panel, you need only look at the portion of the premises served by that panel. In the case of a restaurant, the major electrical work is usually in the kitchen.

Although this method isn't a "magic bullet", it does cut down considerably on the legwork you have to do by eliminating the need to track down individual lighting & receptacle circuits. Use the tables for those, then add in the nameplates for the major loads.

Hope this helps.

Wow, thank you for that! That does help, but still doesn't really answer my original question. What if, for example, I was just renovating a portion of the 5000 SF for a new tenant and the other portion was to still remain in use? And assume they have multiple panelboards, so that getting the overall demand use from the utility won't mean much if we're renovating far enough downstream.

Does that make sense?

Do the same process twice, once for the retained space and a second time for the renovated space. Even though the retained space has existing fixtures & other loads, you can still use the tables for lighting & receptacles. Check the actual nameplate of the existing appliances & other motors in the retained space. There should be a manageable number of those to physically inspect. Add the calculated & nameplate values (remembering to use demand factors where appropriate) to get the total KVA requirement for the retained space.

Repeat the process for the renovation to get the total KVA requirement for that space.

With multiple panelboards, you'll have to repeat that process for each panel in which you intend to add load. If you have several distribution levels (Service Entrance Load Center feeds multiple main panels, which feed multiple sub-panels), you'll have to repeat the process again at every distribution level. The larger the distribution network, the more work involved.

My utility supplies a 220 year old city with a lot of old heavy industry factories. Many of these buildings have been parceled to various tenants after the original manufacturer moved out. We also have many "historic" buildings downtown which have been renovated for multiple uses. My favorite is a 4-story built in 1842 as retail with apartments above. It's now a server farm in the basement, a restaurant on the 1st floor, 2 floors of offices, then topped with an artist community in the penthouse. Of course, none of the tenants arrived at the same time, so we got to do this exercise several times.

If this still doesn't help, email me with more detail about the project. Maybe I'm missing something in translation.

What if, for example, there are multiple 208Y/120Vac panelboards (not multi-section, but separate boards), serving an area? Without drawings, updated panel schedules, or circuit tracing, the only option I see is metering the boards with data loggers.

However, this method seems somewhat new to a lot of our clients. I suspect other engineers in the past may have either ignored it and said the additional load was insignificant, or possibly just kept their calculations to themselves.

He has nailed it down for you. You will need to do some work now. Identify and label all circuits and panel boards. This is your opportunity to shine. Just overcome your inertia. We all have it. When you hit a problem ask the forum. I suggested "Guest" specify a general location.(country) Took some heat for that. This is why. We can show you where to find answers. You can always put an ammeter on the panels and see a typical draw. Quick, easy and cheap.

Good luck,

James

In the worst case you could assume that all breakers which have load connected to them are loaded to 80% of their rating. If that leaves you enough ampacity to add the new load, you are home free.

But this approach overestimates the load so much that it rarely works. I used to have to walk into plants with no drawings and figure where to add load. This was my first step.