Surge Protection Device (SPD) Technology – Benefits & Best Practice!

Figure 1 : T1 & T2 SPD

Phoenix Contact is a global leader in surge protection and is one of the largest manufacturers of surge protective devices (SPD’s) worldwide.  The office in Ireland offers local support for design and applications and is backed up by significant resources from its headquarters in Blomberg, Germany.

The IS10101 Standard

The latest revision of the national wiring rules, I.S 10101:2020 has seen a welcome update to replace the ET 101:2008. Given that it has been 12 years in the waiting, and electrical installations have changed in the meantime, it is not surprising that there have been major updates. This is very welcome when we think about lightning/surge protection as the new standards offer a lot more clarity on the topic.  

Twelve years ago, a typical installation may not include Photovoltaics, LED lighting, LED televisions, home automation, heat pumps etc. etc. and while these are all very welcome advances in technology. They also bring with them new challenges due to the more widespread use of electronics which may make equipment more sensitive. 

Important updates included in standard IS 10101

From a surge protection point of view, here are the main changes.

  • Part 443 – The main update to this section is the inclusion of a risk assessment method to establish a CRL (calculated risk level) for your installation. Good news is that you can avoid carrying out this calculation by installing an SPD.
  • Part 534 – the section has been significantly expanded and has a much-improved section on the selection of SPD’s according the installation location with more detail around practical issues such as the OCPD installation.
  • Part 712 – the section about PV systems, now includes requirements for protection against overvoltage’s and the selection of same.

Practical tips regarding the installation:

Surge protection is simple.  Its function as a device is to control transient overvoltage’s in your electrical system and therefore keep your electrical supply voltage within the limits to which the electrical equipment was designed for. 

To select the correct SPD, you need to consider the following:

  • Installation location
    – Type 1 or Type 2 at the origin / main distribution e.g. Figure 1
    – Type 2 or Type 3 at the sub distribution level and end equipment.  
  • The voltage protection level (Up) – this is the maximum voltage measured during testing and should be less than 2kV* and never greater than the withstand voltage (Uw) of equipment it is connected to. See Figure 2.
  • The maximum continuous operating voltage (Uc) – the SPD must be suitable for the voltage of the supply system.
  • Expected short circuit current – the SCCR value of the SPD must not be less than the prospective short circuit current at its installation location. 


For an SPD to be most effective, proper installation is critical and the connected conductors (A+B+C) must be kept as short and straight as possible.  The line length should be ≤0,5 mtrs. See Figure 3.

  • PE – Conductors used should not be less than;

6mm² copper for Type 2 SPD installed at origin

16mm² copper for Type 1 SPD installed at origin

  • Device protection should be installed as close as possible to the end device.

Preventative Maintenance

To correctly maintain your surge protection, it should be checked at regular intervals and replaced immediately once discovered to be faulty.  Always choose an SPD that has indication on the front which is easily visible. It is also possible to connect remotely where the device is not accessible. 

When using Phoenix Contact surge protection, for preventative maintenance, it is possible to test the SPD with our test equipment; Checkmaster.  

For easy maintenance, it is preferable to use an SPD with a two- piece design i.e. base and element/plug.  This allows the easy replacement of the active component of the SPD without the need to disconnect the wiring, saving money & time, as there is no need to replace the base unit.  Phoenix Contact SEC range of surge protection plugs come with a five-year warranty as standard. 


Q: Is a single pole SPD sufficient for a single-phase supply? 

Ans: Typically, we have a TN-C-S, 3 wire supply in Ireland. This means that a single pole SPD will only provide protection across 2 conductors. Offers possibility for misinterpretation as a typical power socket has only one phase

Q: But Neutral and Earth are at the same potential?

Ans: Under normal conditions this is true but when we talk about surge and lightning events, these are not normal events.  In fact, your electrical equipment is probably more vulnerable to damage from a potential rise on the earth conductor.  Most equipment is not built to withstand a potential difference between earth and neutral.

Q:  My LED lights have failed. Would surge protection be help?

Ans: Absolutely, this is a great example where an SPD can help prolong the life of your electrical system. LED lighting is typically not as robust as old-style filament lamps and so can be prone to overvoltage’s. 

Q:  Do I need to put an MCB in front of my SPD?  

Ans: This depends on the manufacturer and the way you install the SPD, so it is always recommended to check the manufacturer’s instructions.  Phoenix Contact SEC SPD’s do not require any OCPD when the supply fuse is less than 315A gG. 

Q: Can I just turn off the power when we have lightning nearby to protect my equipment? 

Ans:  This will not help. During a lightning event, the earth potential will rise, and this will cause damage.  The only way to prevent damage is to disconnect your device from power supply, but this is not that easy for some devices like e.g. heating system

Q:  Is it possible to monitor your surge protection remotely

Ans:  Yes, there are two ways you can achieve this.  Firstly, every SPD from Phoenix Contact has a relay contact on the SPD which you can connect to whatever you want.   Second, a more advanced option is to connect your SPD to the cloud to be monitored by Phoenix Contact using the Impulse check system.

Q: Is there a standard for SPD’s?

Ans:  Yes, all SPD’s should be manufactured and tested in accordance to IEC 61643-11 and it is important that you check this. If you are not sure, go to the manufacturers website and look for proof. Please note that nearly every manufacturer claims that their SPDs are designed acc. IEC 61643 -11. The only way for the end user to be on the safe side is a certificate that confirms the same.

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