Argument 1: A perfectly balanced Cat. 5 unshielded cable can pass EMC Directive requirements.
3P opinion: Not true.

There is no such thing as perfect balance. But even if you would accept existence of a perfectly balanced cable you could still see EMC failures. Output signals from PC's, etc must also be perfectly balanced and this must apply for all (CE marked) PC's, etc. you intend to use in your LAN for the next many years.

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Argument 2: If balance is fine you do not need shielding.

3P opinion: Not true.

Balance and shielding both affect the EMC performance, and it is agreed by all experts that improvement of balance in principle can reduce requirements to shielding performance (and vice versa).

For unshielded and shielded Cat. 5 cables there are normally only small differences in balance, and consequently the difference in effect of balance on EMC performance is very small. Significance of shielding on EMC performance is very high and cannot be compensated by improving balance.

Generally it is recommended to ask for values of balance (in dB) and not to accept statements like "fine balance". Anything and nothing is "fine".

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Argument 4: Bad shielding is worse than unshielded.

3P opinion: True.

There are a lot of badly shielded LANs due to ignorance of installers and producers. Like UTP cabling such LANs will not pass EMC Directive requirements for generic 100 MHz cabling.

Main problem is bad termination technology between cable and connecting hardware, or a bad EMC design of connecting hardware.

Some simple instructions how to make correctly shielded LANs will be brought later in the 3P Homepage.

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Argument 5: Independent EMC testing of cabling systems can prove compliance to EMC Directive requirements.

3P opinion: Not true.

Any laboratory EMC testing of cabling is fundamentally a testing of the active equipment supported by the cabling.

Test results therefore only concern the active equipment in question (PC's, netcards, etc.), and never concern generic cabling. Don't accept such testing as documentation, unless you want to restrict yourself only to use the specific equipment in your LAN many years ahead.