Sub (service) panel need three or four wires??

[Anonymous]

I need to replace my old service panel which is a 120 amp unit, 45 feet from the main breaker next to the meter, is connected in 1 1/2 inch rigid, with three cables marked with double zeros for what I believe is the cable size, installed in 1959.

In another post concerning a sub panel it was mentioned that it required four cables feeding it . It was also fed with romex. Do I need an extra cable for earth ground or does the pipe count for that?

I just read the post on the water heater and relized I need a disconnect for mine. This is a great site. Thanks in advance for your replies.

Tom

[imported_Ron]

The panel you are working on, is it the main panel with the main disconenct or is it a sub panel (main service disconenct is before the panel)? 00 awg is refered to as 2/0 awg (or two aught).

[Wgoodrich]

Also the mains breaker at the meter 45 feet away, is this inside the same building or is this meter and main breaker on a remote service pole not connected to the building where the panel is located?

You have two sets of design rules that could control your design, two structures rule, or all inside one structure rule.

Curious

Wg

[Anonymous]

The main breakers are on a panel next to the meter on the outside of the house. The meter is on the back because so is the pole its fed from.

The sub-panel is fed from the outside breakers and is located on an inside hallway wall about 18' from the front door. Stright shot in from the door.

I was wrong about the cables feeding the sub-panel. They are marked HABIRSHAW HABIRDURE l TYPE TW 600 V

The cable is a 1/2" thick with the copper part about 5/16" thick.

Again, thanks for your help with this.

[Wgoodrich]

Now we are getting there or at least getting a better picture of what you have. In your design you have a main service rated panel outside by the meter mounted on your outside wall then feeding from that main service rated panel outside to a nonservice rated panel [aka sub-panel] 18' inside your home.

This will require a 4 conductor cable or conduit with 4 single conductors inside that conduit.

Now we need to know what amp rating is your existing main service rated panel. Then we need to know what size non service rated panel you want to install. Then we can give you more info to help you in your designs. If you main service rated panel outside is 200 amp rated then we could install a 200 amp rated sub panel that will increase your power to your home. If your main service rated panel is rated only 100 amps and we installed your 200 amp rated sub panel inside your home from that 100 amp rated main service rated panel then all we did was give you more breakers and spent your money needlessly without gaining power into your home.

What we should do at this point is have you answer the above questions.

What you should do is perform a demand load calculation to find what you need concerning the minimum service size required for you home. Then you can make an informed decision as to how much bigger than minimum service size you want to go. Don't guess this or you may be wasting your money. The following link will provide you with a format to perform your own demand load calculation to find the minimum size. Then we have something to go by better than a guess. Let us know what you find.

http://www.homewiringandmore.com/homewiringusa/2002/definitions/demandcalc02/DwlingDmdCalc02.html

Hope this helps

Wg

[Anonymous]

I checked all of the tags on the appliances and summed them below. It seems high. The main breaker at the rear has two double breakers. One 100 amp pair going to the service panel and a 60 amp pair going stright to the AC unit. This house was built without A/C. That's why the breakers are on the outside for the A/C.

While I am at this project can I replace the main breaaker panel with a unit with more breakers? I would like to feed the pool pump from there since its only ten feet away, and a well pump (1HP motor) this spring. That way I can also use one of those GFI panels for the motors.

I spoke with the Inspector today and he reported they would allow me to pull a permit to do my own work. He quized me a bit and asked how I knew so much if I wasn't an Electrician. He did report that he would be checking my grounding.

Can you tell me if my load calculation is correct? After this I hope we can get figuring out what the fourth cable is for.

Thanks,

Tom

lighting load 220.3A (3VA x 1100 sqaure feet) 3300
Small appliance 220.16.A (3000 VA Small appliance Circuits) 3000
Laundry 220.16.B (1500 VA laundry required) 1500
General lighting 100% of lighting load

A/C, Heating unit 222.21 5.25 HP, 46.67 Amps X 240 Volts =11,200 VA 11200
220.17 Reduced 25%
Water heater Unit tag, 3500 VA 3500 2625
Disposal 1/2 HP 8 Amps X 120 Volt = 960 VA 960 720
Range 14 KW 14000 10500
Pool motor 1 HP 8 Amps X 240 = 1920 VA 1920 1440
Dishwasher 11 Amps X 120 Volts = 1320 VA 1320 990
0

Clothes Dryer 220.18 28 Amps X 240 volts = 6,720 VA
AHJ Minimum 10,000 VA 10000

Microwave 220.19 13 Amps X 120 Volts = 1560 VA 1560

Largest motor 220.22 5.25 Amps X 240 Volts = 1260 X .25% = 315 VA 315

47150 VA
Divided by 240 volts = 194 Amps

The service panel I wanted to use (exact fit) is a 125 amp unit) I missed something here.

[Wgoodrich]

Using the info you supplied the demand load calculated to be 159.8 amp which using 240.6 to size your service would be requiring a minimum service size of 175 amps. Considering the service panels you have available to you a 200 amp main service will be requried. Doubt you will find a 175 amp rated service panel.

You came rather close in your calculation using the format. You did throw one in I would like to know where you got that 10,000 va AHJ? Where did you get that figure in your calculation?

YOU SAID;

lighting load 220.3A (3VA x 1100 sqaure feet) 3300
Small appliance 220.16.A (3000 VA Small appliance Circuits) 3000
Laundry 220.16.B (1500 VA laundry required) 1500
General lighting 100% of lighting load

REPLY;

This is correct up to this point but you missed the general lighting load intermittent load credit of taking the first 3000 va at 100% then the remainder of you non adjusted load would be multiplied times 35% allowing for the intermittent use in a dwelling. This would be you ADJUSTED GENERAL LIGHTING LOADS. You missed this step in your calculation.

YOU SAID;

A/C, Heating unit 222.21 5.25 HP, 46.67 Amps X 240 Volts =11,200 VA 11200

REPLY;
This is fine but if this is a heat pump you would have to combine the air handler plus any heat bank load in your air handler and the heat pump load in your calculation because in the winter all would be used during a heat pump heating process. I did not include any electric heat banks inside your air handler because that was an unknown you did not include.

YOU SAID;
220.17 Reduced 25%

REPLY;
You should do your fastened in place appliances list adding all the va loads as one answer then apply your 25% reduction and only if you have 4 or more fastened in place appliances.

YOU SAID;
Water heater Unit tag, 3500 VA 3500 2625
Disposal 1/2 HP 8 Amps X 120 Volt = 960 VA 960 720

REPLY;
The above are fine as fastened in place appliances with the 25% reduction if four or more total fastened in place appliances.

YOU SAID;
Range 14 KW 14000 10500

REPLY;
220.19 supplies a chart in note four and 210.19 also dictates that you take the name plate rating of a single range but not less than a 40 amp rated appliance load. This would call for 14.4 Kva using 210.19 or using 220.19 you may use the chart that would allow a load of 8.8 Kva. YOu may take the best deal. YOU MUST NOT TAKE A 25% REDUCTION FROM A RANGE.

YOU SAID;
Pool motor 1 HP 8 Amps X 240 = 1920 VA 1920 1440
Dishwasher 11 Amps X 120 Volts = 1320 VA 1320 990
0

REPLY;
These are fine to be listed as fastened in place appliances and using the 25% reduction.

YOU SAID;
Clothes Dryer 220.18 28 Amps X 240 volts = 6,720 VA
AHJ Minimum 10,000 VA 10000

REPLY;
The clothes dryer like the range MUST NOT BE REDUCED 25%. Also you missed a part of the rule in 220.18 that requires that you count the electric clothes dryer at a minimum of 5 Kva even if your name plate rating is less than 5 Kva you must size the load at 100% of the name plate rating but it must be at least 5 Kva rated.

YOU SAID;
Microwave 220.19 13 Amps X 120 Volts = 1560 VA 1560

REPLY;
While I included this without knowing for sure you must be careful when you do or don't include a microwave in your demand load calculation. If this microwave is a sit on the counter plug in anywhere microwave then you DO NOT include this type microwave design in your demand load calculation. If you have a microwave cabinet installed permanently with the cabinets then you have an assigned place for that microwave then you must consider it as a fastened in place appliance and include it with your calculation. You may apply the 25% reduction if you have 4 or more fastened in place appliances in your calculation same as any fastened in place appliance.

YOU SAID;
Largest motor 220.22 5.25 Amps X 240 Volts = 1260 X .25% = 315 VA 315

REPLY;
This is a correct applicatoin to your demand load calculation.

YOU SAID;
The service panel I wanted to use (exact fit) is a 125 amp unit) I missed something here.

REPLY;
You need to look at your main service rated panel outside your home and see if this panel is rated 100 amps or 200 amps. It will say on the nameplate inside the main disconnect as to what amp rating this disconnect has. Also you need to look at the size service entrance conductors connecting between the utility company and to the main service disconnect outside to confirm what size these hot wires are. Tell us what you have in the above question then we can put together your best answer for what you should do with your service.

As for the fourth wire on a sub panel you must have two hot conductors to serve 220 volts then you must have a neutral wire to carry the unbalanced loads of the 120 volt branch circuits back to the center tap of the transformer then you must have the equipment grounding conductor to carry the extremely high voltage faulted ground fault due to short circuits. This fourth wire being an equipment grounding conductor must be separated from the neutral conductor anywhere after the neutral leaves the main service rate panel which in your case is outside by the meter base. This equipment grounding conductor is what saves lives causing the breaker to trip due to interupting rating being the second reason a breaker trips.

Be careful about that pool. There is a whole chapter in the NEC perataing to pool installations being three types of pools. storable pools, permanently installed above ground or inground pools.

Check out the following links concerning pools;

http://www.homewiringandmore.com/homewiringusa/2002/accessory/index.html

Hope this helps

Wg

[Anonymous]

WG,

Thanks for your time on this, I really appreciate it. This started out as a simple question for me and now I really want to update the service the right way.

I checked the main service panel outside. As for a tag I could only find a partial decal and it said 200 am before the rest of it was missing. It looks like the P is almost there.

The panel is directly below the meter and the cables aren't marked. I did measure them and are 1/2" at the insulation and between 5/16 and 3/8 at the copper part. I believe its a size No. 1.

My pool is an inground and existing. I just thought it would be easier to GFI the motor circuit and the future sprinkler pump from the main outside. I thought this would ease the load on the inside service panel (sounds just like the other post on a subpanel). This pool motor is also on two seperate breakers.

As long as we are this far, if we need to change the main service I will. The cost is reasonable and it would be on the same permit. The power company said they would remove meter power if I had a permit.

The equipment grounding connector you mention and I call the fourth wire, is this a ground? I thought the rigid pipe raceway was the ground in this case. Was this grounding connector not always required in the past? I don't mean to pester you, I am just curious.

Thanks,

Tom

[Wgoodrich]

Be careful using the word GROUND this is a generic term that can mean grounded leg [aka neutral on 120 volt circuits] or it can mean an equipment grounding conductor used for short circuit interupting rating of your breaker if a ground faul occurs or it can even mean a true neutral conductor.

Sounds like you already have a 200 amp main service rated panel with 2/0 copper service entrance conductors so you should be fine.

The metal conduit if properly installed all the way between the two panels is listed for use as an equipment grounding conductor and is allowed to take the place of a green or bare equipment grounding conductor.

If this pool pump motor is 220 volt rated then the breaker serving it must be a double pole breaker and not two separate breakers.

The 200 amp service you now have is about 25 amps more than the minimum allowed by the NEC. You should be fine as long as you don't plan on adding too much more load. If you add much load in the future then you may need to increase your service size then. Good news is that you may increase the size of riser and use your existing service conductors adding three more matching size service conductors in the same conduit riser. Then install a new 325 or 400 amp meter base with double lugs then you may continue to use the existing 200 amp main service rated panel and add a second 200 amp main service rated panel creating a parallel 200 amp set of panels using the 6 maximum main disconnect allowance for mains and you would have a 400 amp service using most of the existing equipment only adding a new 200 beside the existing 200 amp main having two main service rated panels with paralell service entrance conductors going from the meter base and the point of connection of the power company. Now you have twice the power but only have the cost than what you were thinking by utilizing the existing main service rated panel in paralell with the new added 200 amp main service rated panel. Sounding better yet? Now you know that you have this money saving option when you need the extra power due to a new future project and now that you know the minimum service size that you have must be a 200 amp service then you can make an informed decision to leave you main service alone being adequate for now with the option to make the service grow in the future if needed. Or you may install the second main service panel now making this new second paralell mains service panel a 40 circuit distribution main service rated panel and wire the swimming pool etc. If you like for any of the panels on or in your home.

Does this help you feel more confident in what you are doing. You did your homework and the guessing is no longer a part of your design. You are getting close to making informed decisions knowing that you have a better knowledge of your system givging you confidence to make a professional decision on your project at this time.

You are not bothering us, we are here to help. If we made you more knowledgable and safer in your wiring designs then we feel like we did something worthwhile. Remember the only bad question is that question that did not get asked.

Congrats you have done your homework !

Let us know how you end up designing your system.

Hope we were of some help to you

Wg

[Anonymous]

WG,

Thanks again for the help. I checked my load calculation and corrected the mistakes. Now my load demand equals yours. I have it now.

The inspector said today it would help if I brought a schedule of the circuits when I apply for the permit.

What exactly is this. I assume its a drawing depicting the box locations, amp size, and the circuits comming from each box.

Am I on the right track? I feel great about this project and couldn't have gone this far without this site.

Tom

[Wgoodrich]

Tom, Go back to the ELECTRIC-HOME forum and look for a post called KITCHEN-GARAGE FORMAT. There is a picture of a drawing this guy made that would make your inspector very impressed if you made a drawing like that example. You can do it on a piece of paper showing your lay out and how the circuits are planned and where you service is and what size service. Then the inspector can take a one minute look and feel comfortable if you both are on the same page in concerning your project. Don't have to make it perfect you are just hand drawing what is called a shop drawing for info only not to scale.

Let us know how you come out.

Wg

[Anonymous]

WG,


Below is my load calculation from what I have learned. Does the microwave get counted twice as I have? I will be going with this for a permit next week again.

let me refresh yuour memory. I have a main service panel out side with two sets of breakers, one 100 amp which feeds the sub panel that handles the whole house, and a 50 amp which connects to the ac unit.

Also will I be able to install a 125 amp sub panel for the whole house hwile leaving the AC unit where it is. I believe from my calculation I will need 124.5 amps. I don't know if this is overloading the sub panel. If it is will a 200 amp panel work with a 150 amp breaker at the main service panel work.

I hope I havn'e confused you. Thanks for your help.

Tom

Demand Load calculation
Tom's House


General Lighting load 230.3A 3VA x 1100 square feet 3300
Small appliance circuit 220.16A 3000 VA 3000
Laundry 220.16B 1500 VA laundry required 1500
Total 7800

General lighting load intermittent load credit, first 3000 VA at 100% 3000
Remaining load at 35% 7800 VA - 3000 VA = 4800 VA x 35% =1680 1680
Ajusted total 4680 4680 VA


A/C Heating unit 220.21 5.25 HP 46.67 x 240 Volts = 11200 VA 11200
Water Heater 220.17 Unit tag reads 3500 VA 3500
Disposal 1/2 HP 8 amps x 120 Volts = 960 VA 960
Microwave (in cabinet) 220.19 13 amps x 240 Volts = 1560 1560
Pool motor 1 HP 8 Amps x 240 Volts = 1920 VA 1920
Diswasher 11 Amps x 120 Volts = 1320VA 1320
Ajusted total 20460

Reduction of 25% for four or more fastened in place appliances 20460 x 0.75 =15345

Ajusted total 15345 15345 VA


Range 220.19 40 Amps x 240 volts = 9600 9600

Clothes dryer 220.18 28 Amps x 240 volts = 6720 6720

Microwave 220.19 13 amps x 240 Volts = 1560 1560

largest motor 220.22 5.25 amps x 240 volts = 1260 x 25% = 315 315

Total 18195 18195


Ajusted total VA 38220 VA

Ajusted total VA divided by 240 = 159.25 Amps

Minimum Service required 240.6 159.25 Amps x 1.1 = 175 Amps
Minimum Service 175 Amps

[Wgoodrich]

Your a/c and heat are not part of the 25% reduction calculation for 4 or more fastened in place appliances they are auto run equipment.

You do not enter microwave more than once unless you have two microwave cabinets.

Your range is required per 220.19 of the NEC to be calculated as one range at 8 kw

Your electric dryer must be calculated a minimum of 5000 watts. Normally load of electric dryers are considered as unknown load using the minimum of 5kw per 220.20 of the NEC.

I recalculated using my new handy IPAQ puter and came up with 148.4 amp demand load calling for a 150 amp service minimum size required. You did pretty good in your calculation.

You most likely will not find your main disconnect outside to be rated for a branch circuit breaker larger than 125 amps. This would be a violation as not large enough to meet minimum size required. If it were me I would change out your existing Main service disconnect and install a main service disconnect 200 amp rated with the branch circuit openings covering your a/c unit and with that new disconnect having what is called a feed through set of lugs at the bottom of the buss bar. Then I would install 2/0 copper from that set of lugs controlled by your 200 amp main breaker in your main disconnect to a new 200 amp sub panel inside using a four wire feeder to that subpanel from that main panel. Then you have enough future to do what may come up and not wasting money setting you up to do it again when you start a new project.

Just my opinion

Wg

[Anonymous]

WG,

I changed my calcs as you suggested but I am still not getting the 150 amp load you got. Please look at my new calculation. I really want ot learn how to do this right.

Thanks again,

Tom

General Lighting load 230.3A 3VA x 1100 square feet 3300.0
Small appliance circuit 220.16A 3000 VA 3000.0
Laundry 220.16B 1500 VA laundry required 1500.0
Total 7800.0

General lighting load intermittent load credit, first 3000 VA at 100% 3000.0
Remaining load at 35% 7800 VA - 3000 VA = 4800 VA x 35% =1680 1680.0
Ajusted total 4680.0 4680.0 VA

Water Heater 220.17 Unit tag reads 3500 VA 3500.0
Disposal 1/2 HP 8 amps x 120 Volts = 960 VA 960.0
Microwave (in cabinet) 220.19 13 amps x 240 Volts = 1560 1560.0
Pool motor 1 HP 8 Amps x 240 Volts = 1920 VA 1920.0
Diswasher 11 Amps x 120 Volts = 1320VA 1320.0
Total 9260.0

Reduction of 25% for four or more fastened in place appliances 9620 x 0.75 =7215

Ajusted total 7215.0 7215.0 VA

Range 220.19 33.3 Amps x 240 volts = 8000 8000.0
Clothes dryer 220.18 20.83 Amps x 240 volts = 5000 5000.0
A/C Heating unit 220.21 5.25 HP 46.67 Amps x 240 Volts = 11200 VA 11200.0
largest motor 220.22 5.25 amps x 240 volts = 1260 x 25% = 315 315.0
Total 24515.0 24515.0 VA

Ajusted total VA 36410.0 VA

Total ajusted VA divided by 240 volts = 151.7 Amps

Minimum Service required 240.6 151.7083333 Total ajusted amps multiplied by 1.1 166.9 Amps

[Wgoodrich]

You are reading into 240.6 more than is supposed to be done. Read the following copied section of the 2002 NEC;

240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted.


All this is saying is that you take the 151 amps demand load you came up with and adjust it up to the next listed size breaker in the above copied rule. There is no such thing as a 151 amp breaker and you are supposed to adjust up making the demand load service minimum size being 175 amp service. Being one amp over 150 I would have accepted 150 amp service as minimum service size. However if you priced a 150 amp service and a 200 amp service you would be better served considering cost and room to grow that a 200 amp service would be your best choice. I suspect you will find little difference in cost and maybe even find the 200 amp service to be cheaper than a 150 amp service due to quatity of 200 amp panels sold rather than the specialty 150 amp panel being more expensive in many occasions.

Hope this helps
Wg

[Anonymous]

yes it does help.

Thanks,

Tom