How Many Computers Can You Put on One Breaker?

The figures we obtain after making calculations result in eight. The order in which we see all the appliances connected adds to our point of view and the month when the current cuts off is not August but January.

We have reached the final price of the system, based upon what is being assumed in order to assign this certain type of label, whether it is essential in a home office or a small computer room.

In short, the circuit rated for 20 A at 120 V has a power output of 2,400 W. The load must equal to or less than 80% of that power output or 1,920 W. The typical office PC along with a monitor consumes anything from 150 W to 300 W. That opens up to the possibility of setting up six to eight workstations. Gaming PCs consume much more than regular computers as some require anywhere between 400 W and 700 W under load. The circuit rated for 15 A has the power output of 1,440 W which is enough for 4-5 office machines. The most surprising thing for many people is not the computers consuming power but the other devices using the same circuit.

The Arithmetic

The reason for this figure of 80% is not precaution in itself. Continuous loads are determined as 125% of running current: in other words, any circuit running at its maximum rating for about three hours will eventually rupture on the weakest link in its chain.

The reason for the “in practice” column being approximately two thirds of the paper number is simple: no one uses just computers. Just one 1,500 W heater takes up up to three-quarters of a 20 A circuit itself and is the most common cause of a trip in a room full of computers during winter.

Why Nameplate Watts Overstate the Load

Power supply rating of a desktop computer shows 500 W, 650 W or 850 W, since these are peak loads and not due to the power consumption required by the machine. The average desktop PC with a power supply rated 80 PLUS will have a power consumption of between 40 W and 80 W when at idle and can reach peaks of 150 to 250 W. A gaming PC with a discrete graphics card takes close to 100 W at idle and can operate between 400 W and 700 W under load conditions.

That is the reason why using the same circuit you can power 8 office computers and 3 gaming computers. A power rating is a theoretical value whereas actual power consumption can be determined with the help of a power meter which is less than the circuit breaker.

A single monitor takes between 20 W and 40 W, a docking station can consume between 10 W and 60 W and a laptop requires a power input between 45 W and 90 W. These values are small independently but they account for 30% of power consumption in an office.

What Else Is on the Circuit

This is where we start to see a mistake in the calculations. Ending up on each of the four points should have a separate line in the calculations:

• Laser printers – A small laser printer takes 300 to 500 watts to print plus spikes beyond 1000 watts when warming up the fuser. Each printer will make a fifth of the15 amps worth by itself.
• Space heaters and kettles – rest at 1500 watts and 1500 to 3000 respectively. Only one of these means any whole computer count is irrelevant.
• Window or portable air conditioners – 900 to 1400 watts of running, compressor inrush equal to five times above.
• UPS equipment – even though consumed loads already count their capacity, after a loss of power, the charging current should also be counted along with the transfer boom when the current passes to the battery.

Any of the above three means we cannot talk about the circuit intended for computers or even intended for computers with any obvious remaining capacity left on it.

Office, Gaming and a Rack

When it comes to office computers, this is much simpler. Eight computers can be powered safely with one circuit rated at 20 A, provided that there are at least two different circuits for printers and no heaters plugged into it.

However, gaming and performance machines will reduce the number of computers that can be plugged in half. On a circuit rated at 20 A, only three to four powerful computers can be connected. What’s more, since the load is variable, it is possible to find a strange combination of events where the circuit is able to pass the ammeter test in the day, but cannot pass it 20 minutes after start-up.

In the case of rack servers, things are different. Each rack server consumes 300 to 600 W and can operate nonstop. This is precisely what the 80% rule refers to. The 20 A circuit can take two or three rack servers at most along with some networking equipment, which means that an electrician should be advised to use a separate circuit rated at 240 V rather than try to squeeze many devices onto a single circuit rated at 120 V.A two-pole device for that arrangement is described in this two-pole miniature circuit breaker, and 240 V halves the current for the same wattage.

What the Circuit Should Look Like for a Home Office

One 20 A dedicated circuit for desks, a separate circuit for the printer and appliances, and a third circuit for lighting in the case of multiple fixtures are sufficient to resolve the dispute over the devices used.

The 20 A circuit in the panel stands for 12 AWG copper wire and a compatible appliance. A standard single-pole 32 to 63 A MCB in a C curve is the usual choice for a mixed electronic load, because the C curve tolerates the inrush of switch-mode supplies without tripping on start-up.

Outbuildings and Converted Rooms

If the workplace is located in a repurposed garage space, a garden room or an external building, the circuits would likely be powered from a separate location rather than the main electrical board.A small board with a main switch and space for four to eight devices, such as this IP65 distribution board, keeps the run short and the protection local.

What Actually Trips, and Why

There are three scenarios, each one having a different reason.

• Trips after a while of normal operation. This is a legitimate overload. The heater has already been triggered. It is worth measuring the current as opposed to what the rating says.
• Trips as soon as any device is on. This is an inrush, usually caused by laser printer fusing or compressor start-up. The most reasonable thing to do is to move the device to another circuit.
• Trips without any devices running. This is due to a faulty device or shared neutral. If there are 2 circuits connected in one branch, there will be unexpected voltage on the devices when the neutral got lost. This is an electrician’s job, not the one of the load calculation.

Also, the circuit breaker might be too old and trips at a lower current than it should. The test for that is described in our breaker FAQ, and it is worth doing before adding circuits that may not be needed.

Measuring Instead of Guessing

The actual amount can be known in three ways, from the cheapest to the most expensive.

The simplest way is to plug everything in into a power meter or other similar device which would directly read the amount of electricity consumed over a week.

Using a clamp meter over a circuit conductor is a little more tricky, though gives the total watt consumption immediately. If you see the reading of below 10 A on something rated for 20 A, you will know you still have headroom, whereas a reading of 16 A means you are at the wire’s limit.

To use the most expensive way, you must perform an LVI on the electric panel after running everything for one hour at maximum load. Our technical service performs the scan and the load survey together, which is usually cheaper than guessing twice.

FAQ

Can I run 2 PCs on one outlet?

Indeed, if two office machines and a monitor consume a total maximum power consumption in the range of 400 W to 600 W then it would be within the capacity of 15 A outlet. Despite that the outlet has a rating of 15 A, it should be noted whether other appliances are consuming power along with above-mentioned appliances or not.

How many computers can run on a 20 amp circuit?

Indeed, if two office machines and a monitor consume a total maximum power consumption in the range of 400 W to 600 W then it would be within the capacity of 15 A outlet. Despite that the outlet has a rating of 15 A, it should be noted whether other appliances are consuming power along with above-mentioned appliances or not.

How many circuits can you run on one breaker?

One circuit gets protected with a single breaker. A tandem breaker combines two independent circuits into the same location, which is a way of saving space,not an increase in capacity, and they are allowed to be used only in panels that are approved for their use.

How many circuits can go on a 200 amp panel?

In terms of physical structure, the number of devices that can fit into the distribution panel typically ranges between 30 and 40. In terms of electrical structure, the number of devices will depend on the capacity of the connected load. A panel that is filled with circuits will be operating close to the limit dictated by its capacity requirements, and to accurately determine whether the panel is filled with devices, a load analysis is needed.

References

• Cerrowire — Ampacity Tables and Circuit Sizing
• NEMA — Branch Circuit and Receptacle Load Guidance
• U.S. Department of Energy — Office Equipment Energy Use
• U.S. Department of Energy — Energy Saver: Electronics
• This Old House — Adding a Dedicated Circuit

Conclusion

A circuit rated for 20 A can support from six to eight office machines, three to four gaming machines, and about two to three servers. Any other load on the circuit reduces the total available load, and in the end, the heater takes the day.

If the demand is larger, it would be better to opt for a dedicated circuit rather than a higher-amp breaker. That allows quoting both the unit and the enclosure simultaneously.