Mandatory for the centralized protection of computer networks

Computers generate leakage current

Each computer is fitted with at least one power supply. The power supply contains capacitors that generate what is known as leakage currents. An international standard limits leakage currents to 3.5 milliamperes (mA). On account of the technology used (high-frequency chopping), the power supply on a computer generates leakage currents close to the authorised maximum, or in other words about 2 mA, typical value for a 200 va computer/network equipment.

Leakage current adds up

The increase in the number of computers and servers connected to an electrical installation is at the root of a sticky problem, the accumulation of leakage currents. Even if each computer, considered individually, complies with the standard, there is nothing to guarantee that once several of them are installed in an office, they will continue to comply. Several computers or other electrical devices, connected to the same circuit-breaker, add up their respective leakage currents. Here, the relevant standard for an electrical installation (NFC 15-100 in France for example) specifies that the total amount may under no circumstances exceed 30 mA. This value is reached with ten computers. Over and above this value, the differential circuit-breaker must trip in order to avoid any risk of electrocution in the event of a fault occurring on one of the devices.
The risk for end-users is that the lights will go out each time they try to turn on the tenth computer.

A real threat

In Europe, some installation standards stipulate that a circuit-breaker should be fitted for every six wall sockets. This is intended to reduce the risks. However, no standard prohibits the use of multi-socket adapters which enable end-users to multiply the number of sockets protected by the same circuit-breaker by a factor of 4 or 5!

The risk is exacerbated by the fact that the circuit-breaker may trip for values as low as 15 mA in order to guarantee tripping at 30 mA. In this case, the risk starts with 5 computers connected to the same circuit-breaker.
Finally, the rise in the number of computers used in business only adds to the danger: each time a new computer (or a peripheral) is connected to a wall socket, the end-user must first check whether the circuit-breaker is capable of coping with the new device.

Overcoming the problem

There are two possible solutions: the first involves asking a specialist to change the electrical installation in order to support high leakage currents. This approach may prove costly, as cables with larger cross-sections will need to be fitted, replacing the existing ones.
The second solution is to use a UPS with galvanic isolation. In exchange for a slight increase, of about 10%, on the price of the UPS, the problem can be completely solved and it is even possible to increase the number of stations connected to the mains without having to re-design the electrical installation.

Advantages of galvanic isolation

As its name suggests, this function completely isolates the UPS output from its input. The only leakage current detected by the head circuit-breaker is the current produced by the UPS itself, that is around 1.5 milliamperes for a Pulsar EX. Galvanic isolation is particularly recommended for a UPS protecting more than 5 to 7 workstations: connected to a wall socket, the UPS allows you to protect an unlimited number of stations without having to worry about disturbances while guaranteeing service continuity.

Which UPSs in the Pulsar range implement galvanic isolation?

Pulsar EX15 to EX40 UPSs have the advantage of offering continuous, high-frequency isolation.
High-frequency technology means that the cost and footprint of the isolation function can be significantly reduced.

And the other UPSs?

The UPSs with the highest power ratings, such as the Comet range for computer rooms, require a visit by an electrician. The electrician will ensure that the circuit-breaker is appropriately rated. Pulsar ES and ESV UPSs, which are designed for distributed protection, do not implement the isolation function. We therefore advise against connecting more than 5 stations to these products. The Pulsar ESV 20, which is theoretically capable of protecting from 15 to 20 computers at a time, is actually recommended for protecting one mini-computer and its immediate peripherals.
Pulsar EX7 and EX10 do not have galvanic isolation as a standard, but as an option, because this will typically protect less than 5 different equipments.

Can a UPS sometimes impair the quality of an electrical installation?

Yes! From an electrical point of view, a UPS is a power supply, just like a computer or a printer. It consequently generates leakage current (about 1.5 milliamperes) which is added to the sum of the leakage currents generated by the protected computer systems, unless there is an isolation system between the UPS input and output. Adding a UPS may be enough to exceed the 15 mA barrier above which the protection on the electrical installation's main circuit-breaker may trip, putting the lights out for all the users.

Galvanic isolation of On-line technology

All the On-line UPSs on the market do not offer this function, even if this was the case ten years ago.
In general, only UPSs with a power rating higher than 1500 va and dedicated to the centralized protection of computer networks in an office environment (« Plug-in ») must imperatively offer galvanic isolation: this is the case for Merlin Gerin Pulsar UPS.
For reasons of cost, some manufacturers offer above 1500 va On-line systems without isolation, while supplying a plug for connection to a wall socket. This is an attempt to reap the benefits of the top-of-the-range image of On-line technology without delivering the quality of service to which users are entitled.