Digital power: a new safety frontier — Part 1
Everyone knows electricity is dangerous — we have strict laws for product compliance and strict regulations for installation to protect lives and property. Communications, on the other hand, was considered relatively safe — “no-one ever got killed by milliamps” was a common sentiment for years.
That’s all about to change. The migration to ‘smart buildings’ is moving virtually every building service to digital, with the Internet of Things (IoT) ‘looming large’ as the great digital disruptor over the next few years, deploying billions of low-cost devices in an ever-increasing range of unique locations and applications. With that proliferation of low power consumption devices, we are seeing a trend, albeit small at present, towards remote powering. Advocates for remote powering claim that one day, everything that is mains-powered in today’s buildings will be remotely powered over communications infrastructure in the not-too-distant future. Riding on the wave of remote powering is the relatively new technology of ‘digital power’. It’s not to be confused with remote powering, but both technologies bring with them a whole new outlook for safety in communications infrastructure.
Consequently, no-one can just assume communications cabling is safe anymore.
Thankfully local and international standards and regulatory bodies are keeping up with these technologies and providing valuable regulation and guidance for our protection. This two-part article explores potential risks associated with remote powering (Part 1) and digital power (Part 2) and the methodologies applied to them through standards, regulations and technology to mitigate these new risks.
Note: The risks discussed here primarily relate to heat and electrocution. There are far more safety risks related to IoT and smart buildings such as life-safety, security and medical systems connected via ICT infrastructure, but that is a completely different risk topic, outside the scope of these articles.
Some people will claim that wireless communications (eg, Wi-Fi, 5G) and wireless power are the future, negating the need for remote powering. But we’ll debunk that myth in Part 2.
We’re seeing a surge in demand for technologies like Power over Ethernet (PoE), Power over HDBaseT (PoH) and new concepts labelled “Digital Ceiling” and “Intrinsically safe office” from the market. As a result, the lines between electrical and communications services are becoming blurred — what was considered safe could now be potentially hazardous and what was considered hazardous could now be potentially safe.
Remote power — of which PoE is a subset — isn’t new. Analog telephones have been remotely powered for over 100 years. Plenty of telephone technicians will tell you of the ‘tingle’ they’d get from the 50 VDC ringtone while working on communications cabling. Today, however, remote power is a very different methodology that safely uses digital communications between the power source equipment (PSE) and the powered device (PD) to control power delivery.
In some cases, PoE is replacing mains power, primarily as a means to converge building services, but with a by-product of reducing the risk of electrocution. Cisco’s Digital Ceiling, for example, promotes an “intrinsically safe” ceiling-grid to power services like lighting and HVAC with extra low voltage (ELV) from an Ethernet switch over communications cabling, rather than mains power from an electrical switchboard. Removing hazardous voltages in the ceiling therefore significantly reduces the risk of electrocution.
Central to remote powering are PoE switches that deliver both data and power over two or four pairs in communications cabling. PoE switches are now the norm — you get the capability whether you want it or not.
And there are plenty of readily available remote-powered products: CCTV surveillance cameras; VoIP phone handsets; LED lighting; wireless access points, HVAC sensors and controllers; PA speakers; access control; audiovisual; and sensors for temperature, light levels, occupancy, motion, moisture, pressure, etc. That’s just the beginning. As IoT matures, we’ll see new remote-powered devices for industrial, agricultural, environmental, scientific, commercial and every sector imaginable flood the market to the point where remote powering becomes the norm. According to a recent MarketsandMarkets report, the PoE market will exceed US$1 billion by 2022.
While manufacturers like Cisco have been promoting PoE for years, industry associations like IEEE have been tempering the rush with standards for interoperability, connectivity and safety. There are several IEEE standards addressing the migration of remote power technologies, the most recent being IEEE802.3bt. It expands the power range up to 90 W, qualifying the power levels and number of pairs used:
- Type 1 – 15.4 W over two pairs (defined by IEEE802.3at)
- Type 2 – 30 W over two pairs (defined by IEEE802.3at)
- Type 3 – 30 W over two pairs
- Type 3 – 60 W over four pairs
- Type 4 – 90 W over four pairs
Ninety watts may not seem hazardous, but low voltage levels on the cabling means the current will be high and could therefore be hazardous. Most cabling standards bodies around the world (ISO, IEC, AS/NZS, TIA, NFPA) are limiting current for remote powering to around 1000 mA per pair. So a PoE system delivering 90 W over all four pairs could likely carry a total of 4 A. That’s significant, not just because of the high current, but because communications cabling wasn’t designed to carry such levels constantly. It was only designed to carry burst energy. And as every electrician and electrical engineer knows, heavy current on small conductors means heat.
So we now have to take steps to mitigate the risks associated with excessive heat in cables, which could be in the vicinity of 15 to 50°C rise above ambient, depending on conductor and cable-bundles. Remote powering also brings many other safety-related issues including arcing at connectors, long-term cable degradation, reduced energy efficiency and reduced transmission performance (especially important in life-safety, security and medical applications). These are very real dangers that are well documented by standards organisations, safety bodies like Underwriters Laboratories (UL) and reputable manufacturers.
To help mitigate safety risks, standards bodies stipulate temperature-rise parameters that, if exceeded, could result in combustion and permanent deformation of cables that would render them permanently inoperable. Maximum cable-bundle sizes; cable routing in catenaries, trays and conduits; cable construction; and conductor diameter to name a few.
The soon-to-be-published cabling regulations — AS/CA S008:2019 (product) and AS/CA S009:2019 (installation) — have extensively addressed remote powering, acknowledging its growing adoption. They’re currently both out for public comment with an accompanying background paper that provides guidance on dealing with remote powering and digital power (referred to as “energy sources” in these and other standards). These documents can be downloaded from www.commsalliance.com.au.
Key points relating to remote powering and digital power in these documents include:
- New requirements for cables, connectors and installation methods to factor greater energies being delivered on the cabling.
- Maximum conductor resistance for cables to ensure their ability to support remote powering. If this cannot be complied with, an ‘engineered solution’ must to be used.
- Cables not to be installed in a manner that would cause a cable’s maximum operating temperature to be exceeded.
- Appendix F in AS/CA S009 describes ES1, ES2 and ES3 energy source classifications, the implications for cablers working on ES1, ES2 and ES3 circuits and the demise of the LV telecommunications circuit classification.
These safety issues were also addressed in numerous presentations at the recent 2019 BICSI conference in Florida. From them, a common thread of recommended practical measures to mitigate risk with remote powering emerged:
- Maximum of 24 cables in a bundle.
- For new PoE-capable cabling installations, use cables with minimum 0.57 mm diameter (23 AWG) conductors.
- For existing cabling being considered for PoE, qualify the cables to have minimum 0.5 mm diameter (24 AWG) conductors as well as other PoE-related characteristics such as minimal DC-resistance unbalance.
- Ensure suppliers provide cable and connectors that are certified for PoE, with substantiating documentation.
- Apply cable-derating for long cable-runs potentially carrying PoE.
In the US, the National Electrical Code (NEC) strictly regulates remote powering for cabling intended to carry more than 60 W. For such situations, the NEC specifies cable criteria (conductor size, current capacity, temperature rating) and installation criteria (cable pathways, bundle sizes, ambient temperatures). These are similar to AS/CA S008 and AS/CA S009, including an engineered solution being required if the prescribed system cannot be practicably delivered.
Recognising the impact of IoT on ICT infrastructure, BICSI has published an Intelligent Buildings standard — BICSI 007‐2017 — that provides comprehensive guidance on designing and installing ICT infrastructure to reliably support remote powering. Adding to the requirements of other standards, this document recommends:
- Equipment cords and fixed cables used for data and power transmission have a minimum conductor diameter of 0.51 mm (24 AWG).
- For new installations, uses cables with 0.64 mm diameter (22 AWG) conductors if:
- Specific building system (eg, audio video systems) is expected to require power exceeding 50 W; and
- Flexibility is required for future systems that could be remote powered.
This brings us to the topic of digital power. Last year, the ACMA mandated a new safety AV and ICT equipment standard (AS/NZS 62368.1:2018). This was a massive change for the communications cabling industry as it introduced energy source classifications ES1, ES2 and ES3 — a key factor in determining safety in digital power. This topic will be discussed in Part 2.
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